diff --git a/firmware/lib/basic/Dtypes.h b/firmware/lib/basic/Dtypes.h
index 5d83f8f..71f7806 100644
--- a/firmware/lib/basic/Dtypes.h
+++ b/firmware/lib/basic/Dtypes.h
@@ -3,19 +3,12 @@
 #ifndef PLATFORM_NATIVE
 
 // ---------------------------------- Arduino -------------------------------------------------------------
-
+#include "Logger.h"
 #include <Arduino.h>
 
 inline void _assert(const char *expression, const char *message, const char *file, int line)
 {
-    Serial.print("Assert ");
-    Serial.print(file);
-    Serial.print(" : ");
-    Serial.print(line);
-    Serial.print("  '");
-    Serial.print(expression);
-    Serial.println("' failed.");
-    Serial.println(message);
+    LOG_WARNING("Assert %s:%d '%s' failed.\n%s", file, line, expression, message);
 }
 
 template <typename T>
diff --git a/firmware/lib/esphttp/EspHttp.h b/firmware/lib/esphttp/EspHttp.h
index 07e0c3e..ad0bd50 100644
--- a/firmware/lib/esphttp/EspHttp.h
+++ b/firmware/lib/esphttp/EspHttp.h
@@ -3,6 +3,7 @@
 #include <esp_http_server.h>
 #include <functional>
 #include "Dtypes.h"
+#include "Logger.h"
 
 constexpr int MAX_URI_HANDLERS = 25;
 
@@ -53,7 +54,7 @@ public:
         .handler = rawCallback,
         .user_ctx = (void *)(&handlerCallbacks_[nextFreeHandler_])};
     if (httpd_register_uri_handler(server_, &uri_endpoint_cfg) != ESP_OK)
-      Serial.println("Failed to register url handler");
+      LOG_WARNING("Failed to register url handler");
     ++nextFreeHandler_;
   }
 
diff --git a/firmware/lib/esphttp/WebDAV.cpp b/firmware/lib/esphttp/WebDAV.cpp
index 5bf583e..214373a 100644
--- a/firmware/lib/esphttp/WebDAV.cpp
+++ b/firmware/lib/esphttp/WebDAV.cpp
@@ -1,5 +1,6 @@
 #include "FilesystemAbstraction.h"
 #include "WebDAV.h"
+#include "Logger.h"
 
 namespace webdav_constants
 {
@@ -93,7 +94,7 @@ size_t webdavFileListingSpiffs(char *buffer, size_t maxLength,
     toBuffer(MULTISTATUS_END);
 
     if (incomplete)
-        Serial.println("WebDAV listing response is incomplete, because buffer was too small");
+        LOG_WARNING("WebDAV listing response is incomplete, because buffer was too small");
     return bytesWritten;
 }
 
@@ -122,7 +123,7 @@ std::function<void(httpd_req_t *)> webdavHandler(const char *uriPrefix,
         case HTTP_GET:
         {
             auto filename = uriToFileName(uri, spiffsFolder);
-            Serial.printf("GET filename %s\n", filename.c_str());
+            LOG_INFO("GET filename %s", filename.c_str());
             auto file = portablefs::open(filename.c_str(), "r");
             if (file.available())
             {
@@ -154,14 +155,14 @@ std::function<void(httpd_req_t *)> webdavHandler(const char *uriPrefix,
         }
         case HTTP_OPTIONS:
         {
-            Serial.println("Options request");
+            LOG_INFO("Options request");
             httpd_resp_set_status(req, "204 No Content");
             httpd_resp_set_hdr(req, "Access-Control-Allow-Methods", "GET, PROPFIND, DELETE, OPTIONS");
             httpd_resp_send(req, "", 0);
             break;
         }
         default:
-            Serial.printf("Sending 404 %d uri %s\n", req->method, req->uri);
+            LOG_INFO("Sending 404 %d uri %s", req->method, req->uri);
             httpd_resp_send_404(req);
         }
     };
diff --git a/firmware/lib/logging/Logger.cpp b/firmware/lib/logging/Logger.cpp
new file mode 100644
index 0000000..fc1ef3d
--- /dev/null
+++ b/firmware/lib/logging/Logger.cpp
@@ -0,0 +1,50 @@
+#include "Logger.h"
+
+constexpr size_t LOG_SIZE = 1024 * 1024 * 2;
+
+static Logger *theLogger = nullptr;
+
+Logger *Logger::getInstance()
+{
+  return theLogger;
+}
+
+void Logger::init()
+{
+  theLogger = new Logger();
+  Serial.begin(115200);
+  while (!Serial)
+  {
+  }
+}
+
+Logger::Logger()
+{
+  data_ = (char *)heap_caps_malloc(LOG_SIZE, MALLOC_CAP_SPIRAM);
+  totalSize_ = LOG_SIZE;
+  currentSize_ = 0;
+
+  // write header placeholder
+  const auto millisPlaceholder = 0;
+  memcpy(&data_[currentSize_], &millisPlaceholder, sizeof(millisPlaceholder));
+  currentSize_ += sizeof(millisPlaceholder);
+
+  NtpTimeT ntpPlaceholder = 0;
+  memcpy(&data_[currentSize_], &ntpPlaceholder, sizeof(ntpPlaceholder));
+  currentSize_ += sizeof(ntpPlaceholder);
+}
+
+void Logger::setNtpTime(NtpTimeT ntpTime)
+{
+  auto data = getInstance()->data_;
+
+  const auto millisTime = millis();
+  memcpy(&data[0], &millisTime, sizeof(millisTime));
+  memcpy(&data[sizeof(millisTime)], &ntpTime, sizeof(ntpTime));
+}
+
+
+Logger::~Logger()
+{
+  free(data_);
+}
\ No newline at end of file
diff --git a/firmware/lib/logging/Logger.h b/firmware/lib/logging/Logger.h
new file mode 100644
index 0000000..68285b0
--- /dev/null
+++ b/firmware/lib/logging/Logger.h
@@ -0,0 +1,62 @@
+#pragma once
+
+#include "Arduino.h"
+
+#define LOG_INFO(...)                        \
+  {                                          \
+    Logger::getInstance()->log(__VA_ARGS__); \
+  }
+
+#define LOG_TRACE(...)                       \
+  {                                          \
+    Logger::getInstance()->log(__VA_ARGS__); \
+  }
+
+#define LOG_WARNING(...)                     \
+  {                                          \
+    Logger::getInstance()->log(__VA_ARGS__); \
+  }
+
+class Logger
+{
+public:
+  using NtpTimeT = unsigned long;
+
+  ~Logger();
+
+  template <class... Args>
+  inline bool log(const char *formatStr, Args &&...args)
+  {
+    const auto time = millis();
+
+    if (totalSize_ - currentSize_ <= sizeof(time))
+      return false;
+
+    memcpy(&data_[currentSize_], &time, sizeof(time));
+    currentSize_ += time;
+
+    const auto spaceLeft = totalSize_ - currentSize_;
+    auto charsWritten = snprintf(&data_[currentSize_], spaceLeft, formatStr,
+                                 std::forward<Args>(args)...);
+    Serial.println(&data_[currentSize_]);
+
+    if (charsWritten < spaceLeft)
+    {
+      currentSize_ += charsWritten;
+      return true;
+    }
+    else
+      return false;
+  }
+
+  static Logger *getInstance();
+  static void init();
+  static void setNtpTime(NtpTimeT time);
+
+private:
+  Logger();
+
+  char *data_;
+  size_t totalSize_;
+  size_t currentSize_;
+};
diff --git a/firmware/lib/scale/Scale.h b/firmware/lib/scale/Scale.h
index 5ef5c6d..9343286 100644
--- a/firmware/lib/scale/Scale.h
+++ b/firmware/lib/scale/Scale.h
@@ -7,8 +7,10 @@ class Scale
 public:
     bool measure(uint16_t &measurementOut)
     {
-        long value = hx711_.read_average(CONFIG_MEASUREMENT_AVG_COUNT) - offset_;
-        Serial.println(value);
+        long value = hx711_.read_average(CONFIG_MEASUREMENT_AVG_COUNT);
+        LOG_TRACE("rv %ld\n", value);
+        value -= offset_;
+        
         if (value < 0)
             measurementOut = (int16_t)(-(value >> valueRightShift_ ));
         else
@@ -24,9 +26,9 @@ public:
 
     void tare(uint32_t numMeasurementsToAverage = 50)
     {
-        hx711_.read_average(3);
+        auto v1 = hx711_.read_average(3);
         offset_ = hx711_.read_average(numMeasurementsToAverage);
-        Serial.printf("Tare offset %ld\n", offset_);
+        LOG_INFO("Init reading %ld, Tare offset %ld\n", v1, offset_);
     }
 
     const long &offset() const { return offset_; }
diff --git a/firmware/lib/session/MeasurementSession.h b/firmware/lib/session/MeasurementSession.h
deleted file mode 100644
index 08c828b..0000000
--- a/firmware/lib/session/MeasurementSession.h
+++ /dev/null
@@ -1,139 +0,0 @@
-#include "SessionChunk.h"
-
-
-template<typename Measurement_T, typename Reader, typename Writer, uint32_t CHUNK_SIZE>
-class MeasurementSession {
-public:
-    typedef SessionChunk<Measurement_T, CHUNK_SIZE> Chunk_T;
-
-    MeasurementSession()
-            : currentChunk(&chunks[0]),
-              otherChunk(&chunks[1]) {}
-
-    void init(uint32_t epochStartTime) {
-        currentChunk = &chunks[0];
-        otherChunk = &chunks[1];
-        currentChunk->init(epochStartTime, 0);
-        otherChunk->init(0, 0);
-    }
-
-    bool addPoint(Measurement_T measurement) {
-        const bool successful = currentChunk->addPoint(measurement);
-        if (!successful) {
-            Serial.println("Starting session rotate");
-            rotate();
-            const bool secondInsertSuccess = currentChunk->addPoint(measurement);
-            assert_msg(secondInsertSuccess, "Session: insertion after rotation failed");
-            // TODO check that there is place for file - remove old files
-        }
-        return true;
-    }
-
-    void finalize() {
-        if( otherChunkFilled() )
-            saveChunkToFile(otherChunk);
-        if( currentChunk->numMeasurements() > 0) {
-            saveChunkToFile(currentChunk);
-        }
-        currentChunk->init(0, 0);
-        otherChunk->init(0, 0);
-    }
-
-    uint32_t numMeasurements() const {
-        return currentChunk->getStartIndex() + currentChunk->numMeasurements();
-    }
-
-    template<typename Encoder_T>
-    void serialize(Encoder_T & encoder, uint32_t startIdx) const
-    {
-        const uint32_t lastIdx = currentChunk->getStartIndex() + currentChunk->numMeasurements();
-        if( lastIdx <= startIdx) {
-            encoder.template sendArray<Measurement_T>(nullptr, 0);
-            return;
-        }
-
-        Chunk_T::sendHeader(encoder, currentChunk->getStartTime(), startIdx);
-        encoder.template sendArrayHeader<Measurement_T>(lastIdx - startIdx);
-        while(startIdx < lastIdx)
-            startIdx = serializeChunk(encoder, startIdx);
-        assert_msg(startIdx == lastIdx, "Not all data was sent");
-    }
-
-    uint32_t getStartTime() const {
-        return currentChunk->getStartTime();
-    }
-private:
-    void rotate() {
-        if( otherChunkFilled() )
-            saveChunkToFile(otherChunk);
-        swapChunks();
-
-        currentChunk->init(otherChunk->getStartTime(), otherChunk->getStartIndex() + CHUNK_SIZE);
-    }
-
-    bool otherChunkFilled() const {
-        return otherChunk->numMeasurements() > 0;
-    }
-
-    void swapChunks() {
-        Chunk_T *tmp = currentChunk;
-        currentChunk = otherChunk;
-        otherChunk = tmp;
-    }
-
-    void saveChunkToFile(Chunk_T *chunk) const {
-        const uint32_t chunkNr = chunk->getStartIndex() / CHUNK_SIZE;
-        const auto fileName = chunkFileName(chunkNr, chunk->getStartTime());
-        Serial.print("Writing session to file ");
-        Serial.println(fileName);
-        Writer writer(fileName);
-        chunk->serialize(writer.encoder());
-    };
-
-    template< typename Encoder_T>
-    uint32_t serializeChunk(Encoder_T & encoder, uint32_t startIdx) const {
-        assert_msg( startIdx < currentChunk->getStartIndex() + currentChunk->numMeasurements(),
-                   "serializeChunk: invalid startIdx" );
-
-        if( startIdx >= currentChunk->getStartIndex() ) {
-            const auto localStartIdx = startIdx - currentChunk->getStartIndex();
-            const auto numElements = currentChunk->numMeasurements() - localStartIdx;
-            assert_msg(numElements <= currentChunk->numMeasurements(), "Internal problem in serializeChunk");
-            encoder.sendArrayPartialContents( currentChunk->getDataPointer() + localStartIdx, numElements );
-            return currentChunk->getStartIndex() + currentChunk->numMeasurements();
-        } else if( startIdx >= otherChunk->getStartIndex() && otherChunkFilled() ) {
-            encoder.sendArrayPartialContents( otherChunk->getDataPointer(), otherChunk->numMeasurements() );
-            assert_msg( otherChunk->numMeasurements(), CHUNK_SIZE );
-            return otherChunk->getStartIndex() + otherChunk->numMeasurements();
-        } else {
-            if( encoder.getSizeCountMode() ) {
-                encoder.template sendArrayPartialContents<Measurement_T>(nullptr, CHUNK_SIZE);
-            } else {
-                const uint32_t chunkNr = startIdx / CHUNK_SIZE;
-                const auto chunkFileNameStr = chunkFileName(chunkNr, currentChunk->getStartTime());
-                Reader reader(chunkFileNameStr);
-                reader.seek(Chunk_T::valueOffset());
-
-                const uint32_t PART_SIZE = 32;
-#ifndef ARDUINO
-                static_assert((PART_SIZE < CHUNK_SIZE) && (CHUNK_SIZE % PART_SIZE == 0));
-#endif
-                Measurement_T buffer[PART_SIZE];
-                for(uint32_t i = 0; i < CHUNK_SIZE; i += PART_SIZE)
-                {
-                    reader.readBytes((char*) buffer, sizeof(Measurement_T) * PART_SIZE);
-                    encoder.template sendArrayPartialContents<Measurement_T>(buffer, PART_SIZE);
-                }
-            }
-            return startIdx + CHUNK_SIZE;
-        }
-    }
-
-    static String chunkFileName(uint32_t chunkNr, uint32_t startTime) {
-        return("/dat/" + toString(startTime) + String("_") + toString(chunkNr));
-    }
-
-    Chunk_T chunks[2];
-    Chunk_T *currentChunk;
-    Chunk_T *otherChunk;
-};
diff --git a/firmware/lib/session/SessionManager.h b/firmware/lib/session/SessionManager.h
index 51f9667..65ee357 100644
--- a/firmware/lib/session/SessionManager.h
+++ b/firmware/lib/session/SessionManager.h
@@ -5,6 +5,7 @@
 #include <NTPClient.h>
 
 #include "AutoStartStop.h"
+#include "Logger.h"
 
 template <typename SessionT>
 class SessionManager
@@ -32,7 +33,8 @@ public:
     void enableAutoStop(bool enable) { autoStop_.enable(enable); }
     bool autoStartEnabled() const { return autoStart_.enabled(); };
     bool autoStopEnabled() const { return autoStop_.enabled(); }
-
+    
+    unsigned long getNtpTime() { return timeClient_.getEpochTime(); } 
 private:
     void onMeasurementTaken(MeasurementType measurement);
 
@@ -69,10 +71,10 @@ void SessionManager<SessionT>::tare()
 {
     if (measuring_)
         stopMeasurements();
-    Serial.println("Beginning tare");
+    LOG_INFO("Beginning tare");
     scale_.begin(scaleDoutPin_, scaleSckPin_, valueRightShift_);
     scale_.tare(CONFIG_TARE_AVG_COUNT);
-    Serial.println("Finished tare");
+    LOG_INFO("Finished tare");
 }
 
 template <typename SessionT>
@@ -135,7 +137,7 @@ void SessionManager<SessionT>::iteration()
         else
         {
             const long skipped = (cycleDuration / CONFIG_MEASURE_DELAY);
-            Serial.printf("Measurements skipped: %ld, cycleDuration %ld\n", skipped, cycleDuration);
+            LOG_WARNING("Measurements skipped: %ld, cycleDuration %ld", skipped, cycleDuration);
 
             for (int i = 0; i < skipped; ++i)
                 onMeasurementTaken(measurement);
@@ -154,7 +156,7 @@ void SessionManager<SessionT>::onMeasurementTaken(MeasurementType measurement)
         bool autoStop = autoStop_.autoStop(measurement);
         if (autoStop)
         {
-            Serial.println("Auto stop");
+            LOG_INFO("Auto stop");
             stopMeasurements();
             return;
         }
@@ -162,7 +164,7 @@ void SessionManager<SessionT>::onMeasurementTaken(MeasurementType measurement)
         bool addPointSuccessful = session_.addPoint(measurement);
         if (!addPointSuccessful)
         {
-            Serial.println("Maximum time of session reached - stopping");
+            LOG_INFO("Maximum time of session reached - stopping");
             stopMeasurements();
             return;
         }
@@ -171,7 +173,7 @@ void SessionManager<SessionT>::onMeasurementTaken(MeasurementType measurement)
     {
         if (autoStart_.autoStart(measurement))
         {
-            Serial.println("Auto start");
+            LOG_INFO("Auto start");
             startMeasurements();
             return;
         }
diff --git a/firmware/lib/session/SimpleMeasurementSession.h b/firmware/lib/session/SimpleMeasurementSession.h
index c40261a..2d1984d 100644
--- a/firmware/lib/session/SimpleMeasurementSession.h
+++ b/firmware/lib/session/SimpleMeasurementSession.h
@@ -1,6 +1,8 @@
 #include "Dtypes.h"
 #include "SessionChunk.h"
 #include "FilesystemAbstraction.h"
+#include "Logger.h"
+
 
 template <typename Measurement_T, uint32_t MAX_SIZE>
 class SimpleMeasurementSession
@@ -37,7 +39,7 @@ public:
         if (success && (chunk->numMeasurements() % saveInterval_) == 0)
             saveToFileSystem();
         if (!success)
-            Serial.println("Failed to add point");
+            LOG_WARNING("Failed to add point");
         return success;
     }
 
@@ -79,9 +81,9 @@ private:
 
         // todo: check this! free doesn't mean that the file writing actually works ok
         // use error codes of write instead? anyway: test it!
-        Serial.printf("%ld saveToFileSystem start\n", millis());
+        LOG_INFO("%ld saveToFileSystem start", millis());
         deleteUntilBytesFree(CONFIG_SESSION_MAX_SIZE);
-        Serial.printf("   %ld after deleteUntilBytesFree()\n", millis());
+        LOG_INFO("   %ld after deleteUntilBytesFree()", millis());
 
         String filename = String(CONFIG_DATA_PATH) + "/" + String(chunk->getStartTime());
         if (portablefs::exists(filename.c_str()))
@@ -104,7 +106,7 @@ private:
             StreamingMsgPackEncoder<portablefs::File> encoder(&file);
             chunk->serialize(encoder);
         }
-        Serial.printf("   %ld saveToFileSystem done\n", millis());
+        LOG_INFO("   %ld saveToFileSystem done", millis());
     }
 
     void deleteUntilBytesFree(size_t requiredSpace)
@@ -132,7 +134,7 @@ private:
             }
             assert(nextSessionToDelete > 0);
             assert(nextSessionToDelete < uint32_t(-1));
-            Serial.printf("Removing old session %s to make space\n", filenameToDelete.c_str());
+            LOG_INFO("Removing old session %s to make space", filenameToDelete.c_str());
             portablefs::remove(filenameToDelete.c_str());
             auto newFreeBytes = portablefs::totalBytes() - portablefs::usedBytes();
             assert(newFreeBytes > freeBytes);
diff --git a/firmware/lib/session/SpiffsStorage.h b/firmware/lib/session/SpiffsStorage.h
deleted file mode 100644
index 0053c96..0000000
--- a/firmware/lib/session/SpiffsStorage.h
+++ /dev/null
@@ -1,90 +0,0 @@
-#pragma once
-#include "StreamingMsgPackEncoder.h"
-#include "FilesystemAbstraction.h"
-
-#ifdef USE_ESP32 
-
-struct WriterAdaptor 
-{
-    File * f;
-    void write(const char * ptr, size_t size) {
-        f->write(reinterpret_cast<const uint8_t *>(ptr), size);
-    }
-};
-
-class SpiffsStorageWriter {
-public:
-    SpiffsStorageWriter(const String &fileName) :
-            f_(SPIFFS.open(fileName, "w")),
-            adaptor_{&f_},
-            encoder_(&adaptor_),
-            fileName_(fileName)
-    {
-        bool success = f_;
-        Serial.println(success);
-    }
-    ~SpiffsStorageWriter() {
-        f_.close();
-        Serial.println(fileName_);
-        Serial.println(SPIFFS.exists(fileName_));
-    }
-    StreamingMsgPackEncoder<WriterAdaptor> &encoder() { return encoder_; }
-
-private:
-    File f_;
-    WriterAdaptor adaptor_;
-    StreamingMsgPackEncoder<WriterAdaptor> encoder_;
-    String fileName_;
-};
-
-#else 
-
-class SpiffsStorageWriter {
-public:
-    SpiffsStorageWriter(const String &fileName) :
-            f_(SPIFFS.open(fileName, "w")),
-            encoder_(&f_),
-            fileName_(fileName)
-    {
-        bool success = f_;
-        Serial.println(success);
-    }
-    ~SpiffsStorageWriter() {
-        f_.close();
-        Serial.println(fileName_);
-        Serial.println(SPIFFS.exists(fileName_));
-    }
-    StreamingMsgPackEncoder<File> &encoder() { return encoder_; }
-
-private:
-    File f_;
-    StreamingMsgPackEncoder<File> encoder_;
-    String fileName_;
-};
-
-#endif
-
-
-
-
-
-class SpiffsStorageReader
-{
-public:
-    SpiffsStorageReader(const String &fileName) :
-            f_(SPIFFS.open(fileName, "r"))
-    {}
-    ~SpiffsStorageReader() {
-        f_.close();
-    }
-
-    uint32_t readBytes(char *buffer, size_t length) {
-        return f_.readBytes(buffer, length);
-    }
-
-    bool seek(uint32_t pos) {
-        return f_.seek(pos);
-    }
-private:
-    File f_;
-};
\ No newline at end of file
diff --git a/firmware/lib/session/StreamingMsgPackEncoder.h b/firmware/lib/session/StreamingMsgPackEncoder.h
index 82f0343..ba39e40 100644
--- a/firmware/lib/session/StreamingMsgPackEncoder.h
+++ b/firmware/lib/session/StreamingMsgPackEncoder.h
@@ -60,7 +60,7 @@ public:
     {
         auto len = strlen_P(s);
         if( len >= 255 ) {
-            Serial.println(F("ERROR: StreamingMsgPackEncoder::string255 - string too long"));
+            LOG_WARNING("ERROR: StreamingMsgPackEncoder::string255 - string too long");
             return;
         }
         byte castedLen = (byte)(len);
diff --git a/firmware/lib/webdav/AsyncWebDav.h b/firmware/lib/webdav/AsyncWebDav.h
deleted file mode 100644
index a45fbd4..0000000
--- a/firmware/lib/webdav/AsyncWebDav.h
+++ /dev/null
@@ -1,237 +0,0 @@
-#include <ESPAsyncWebServer.h>
-#include "FilesystemAbstraction.h"
-
-
-#define FLASH_TEXT(name) const char *name
-
-namespace webdav_constants
-{
-    FLASH_TEXT(MULTISTATUS_START) = "<?xml version=\"1.0\" ?><D:multistatus xmlns:D=\"DAV:\">";
-    FLASH_TEXT(MULTISTATUS_END) = "</D:multistatus>";
-    FLASH_TEXT(RESPONSE_START) = "<D:response>";
-    FLASH_TEXT(RESPONSE_END) = "</D:response>\n";
-    FLASH_TEXT(HREF_START) = "<D:href>";
-    FLASH_TEXT(HREF_END) = "</D:href>";
-    FLASH_TEXT(PROPSTAT_START) = "<D:propstat>";
-    FLASH_TEXT(PROPSTAT_END) = "</D:propstat>";
-    FLASH_TEXT(PROP_START) = "<D:prop>";
-    FLASH_TEXT(PROP_END) = "</D:prop>";
-    FLASH_TEXT(RESOURCETYPE_START) = "<D:resourcetype>";
-    FLASH_TEXT(RESOURCETYPE_END) = "</D:resourcetype>";
-    FLASH_TEXT(RESOURCE_COLLECTION) = "<D:collection/>";
-    FLASH_TEXT(HTTP_204_NO_CONTENT) = "HTTP/1.1 204 No Content";
-
-    FLASH_TEXT(CONTENTLEN_START) = "<D:getcontentlength>";
-    FLASH_TEXT(CONTENTLEN_END) = "</D:getcontentlength>";
-    FLASH_TEXT(CREATEDATE_START) = "<D:creationdate>";
-    FLASH_TEXT(CREATEDATE_END) = "</D:creationdate>";
-    FLASH_TEXT(MODDATE_START) = "<D:getlastmodified>";
-    FLASH_TEXT(MODDATE_END) = "</D:getlastmodified>";
-    FLASH_TEXT(STATUS_OK) = "<D:status>HTTP/1.1 200 OK</D:status>";
-} // namespace webdav_constants
-
-class WebdavFileListCallback
-{
-public:
-    WebdavFileListCallback(const String &path)
-        : path_(path), headerWritten_(false), finished_(false)
-    {
-        dir_ = portablefs::openDir(path);
-    }
-
-    size_t operator()(uint8_t *buffer, size_t maxLen, size_t index)
-    {
-        Serial.printf("%ld index %u\n", millis(), index);
-
-        using namespace webdav_constants;
-        uint8_t *bufferStart = buffer;
-
-        if (finished_)
-            return 0;
-
-        if (!headerWritten_)
-        {
-            toBuffer(buffer, MULTISTATUS_START);
-            headerWritten_ = true;
-        }
-
-        bool fileFound = false;
-        Serial.printf("%ld (0)\n", millis());
-        while (dir_.next())
-        {
-            if (isFirstFileOfTrainingGroup())
-            {
-                fileFound = true;
-                break;
-            }
-        }
-
-        if (fileFound)
-        {
-            //toBuffer(buffer, path_.c_str());
-            toBuffer(buffer, RESPONSE_START);
-            toBuffer(buffer, HREF_START);
-            Serial.printf("%ld (1)\n", millis());
-            const auto fileName = dir_.fileName();
-            const auto fileNameWithoutDir = fileName.substring(fileName.lastIndexOf("/") + 1);
-            String fileBaseName = fileNameWithoutDir.substring(0, fileNameWithoutDir.indexOf('_'));
-            fileBaseName += ".st";
-            Serial.printf("%ld (2)\n", millis());
-            toBuffer(buffer, fileBaseName.c_str());
-            toBuffer(buffer, HREF_END);
-            toBuffer(buffer, PROPSTAT_START);
-            toBuffer(buffer, PROP_START);
-            if (dir_.isDirectory())
-            {
-                toBuffer(buffer, RESOURCETYPE_START);
-                toBuffer(buffer, RESOURCE_COLLECTION);
-                toBuffer(buffer, RESOURCETYPE_END);
-            }
-            else
-            {
-                toBuffer(buffer, CONTENTLEN_START);
-                String fileSizeStr(getFileSize(fileName));
-                //toBuffer(buffer, fileSizeStr.c_str());
-                toBuffer(buffer, "1");
-                toBuffer(buffer, CONTENTLEN_END);
-            }
-            Serial.printf("%ld (3)\n", millis());
-
-            toBuffer(buffer, PROP_END);
-            toBuffer(buffer, STATUS_OK);
-            toBuffer(buffer, PROPSTAT_END);
-            toBuffer(buffer, webdav_constants::RESPONSE_END);
-        }
-        else
-        {
-            toBuffer(buffer, MULTISTATUS_END);
-            finished_ = true;
-        }
-
-
-        size_t bytesWritten = buffer - bufferStart;
-        assert_msg(bytesWritten < maxLen, "Written too much!");
-        Serial.printf("%ld Bytes written %u\n", millis(), bytesWritten);
-        //Serial.print("Max bytes ");
-        //Serial.println(maxLen);
-        return bytesWritten;
-    }
-
-private:
-    bool isFirstFileOfTrainingGroup()
-    {
-        return !dir_.isDirectory() && dir_.fileName().endsWith("_0");
-    }
-
-    size_t getFileSize(const String &fileZero)
-    {
-        size_t size = 0;
-        auto fileBase = fileZero.substring(0, fileZero.indexOf('_'));
-        auto newDirInstance = portablefs::openDir(path_);
-        while (newDirInstance.next())
-            if (newDirInstance.isFile() && newDirInstance.fileName().startsWith(fileBase))
-                size += newDirInstance.fileSize();
-        return size;
-    }
-
-    void toBuffer(uint8_t *&buffer, const char *text)
-    {
-        auto len = strlen(text);
-        memcpy(buffer, text, len);
-        buffer += len;
-    }
-
-    portablefs::Dir dir_;
-    const String path_;
-    bool headerWritten_;
-    bool finished_;
-};
-
-bool deleteMeasurementFiles(const String &stName, const String &folder)
-{
-    String baseName = folder + "/" + stName.substring(0, stName.indexOf("."));
-    int counter = 0;
-    {
-        auto d = portablefs::openDir(folder);
-        while (d.next())
-            if (d.isFile() && d.fileName().startsWith(baseName))
-                ++counter;
-    }
-    if (counter == 0)
-        return false;
-
-    for (int i = 0; i < counter; ++i)
-    {
-        const String pathToDelete = baseName + "_" + String(i);
-        if (!SPIFFS.remove(pathToDelete))
-            return false;
-    }
-    return true;
-}
-
-class SpiffsWebDavHandler : public AsyncWebHandler
-{
-public:
-    SpiffsWebDavHandler(const String &prefix, const String &folder)
-        : prefix_(prefix), folder_(folder)
-    {
-    }
-
-    virtual bool canHandle(AsyncWebServerRequest *request) override final
-    {
-        Serial.print("Can handle for url : ");
-        Serial.println(request->url());
-        return request->url().startsWith(prefix_);
-    }
-
-    virtual void handleRequest(AsyncWebServerRequest *request) override final
-    {
-        if (request->url() == prefix_ + "/" && (request->method() == HTTP_GET || request->method() == HTTP_PROPFIND))
-        {
-            // send chunked response - it is too large to send in one go
-            auto response = request->beginChunkedResponse("application/xml",
-                                                          WebdavFileListCallback(folder_));
-            request->send(response);
-        } /* 
-        else if(request->url() == prefix_ + "/" && request->method() == HTTP_GET) {
-            AsyncResponseStream * response = request->beginResponseStream("text/plain", 1460*10);
-            Dir dir = SPIFFS.openDir(folder_);
-            Serial.print("Opening folder ");
-            Serial.println(folder_);
-            while (dir.next()) {
-                Serial.print("  File: ");
-                Serial.println(dir.fileName());
-                response->println(dir.fileName());
-            }
-            request->send(response);
-        }*/
-        else if (request->method() == HTTP_GET)
-        {
-            auto path = folder_ + request->url().substring(prefix_.length());
-            if (SPIFFS.exists(path))
-                request->send(SPIFFS, path, "application/x-msgpack");
-            else
-                request->send(404, "text/plain", "Webdav: File not found");
-        }
-        else if (request->method() == HTTP_DELETE)
-        {
-            auto stFileName = request->url().substring(prefix_.length() + 1);
-            Serial.print("HTTP_DELETE for ");
-            Serial.println(stFileName);
-            bool deleteSuccessful = deleteMeasurementFiles(stFileName, folder_);
-            if (deleteSuccessful)
-                request->send(204, "text/plain", "Success");
-            else
-                request->send(404, "text/plain", "Webdav: File to delete not found");
-        }
-        else
-        {
-            request->send(404, "text/plain", "Webdav: Invalid request");
-        }
-    }
-    virtual bool isRequestHandlerTrivial() override final { return false; }
-
-private:
-    String prefix_;
-    String folder_;
-};
diff --git a/firmware/lib/wifimanager/WifiManager.cpp b/firmware/lib/wifimanager/WifiManager.cpp
index 4def673..78b1c07 100644
--- a/firmware/lib/wifimanager/WifiManager.cpp
+++ b/firmware/lib/wifimanager/WifiManager.cpp
@@ -1,4 +1,5 @@
 #include "WifiManager.h"
+#include "Logger.h"
 
 void WifiManager::begin(const String &hostname, const String & wifiStaModeName)
 {
@@ -21,7 +22,7 @@ void WifiManager::startWifi()
     // station mode
     WiFi.mode(WIFI_STA);
     WiFi.begin(staSSID.c_str(), staPassword.c_str());
-    Serial.printf("Starting WiFi station mode to ssid %s, hostname %s\n", staSSID.c_str(), hostname_.c_str());
+    LOG_INFO("Starting WiFi station mode to ssid %s, hostname %s", staSSID.c_str(), hostname_.c_str());
     WiFi.setHostname(hostname_.c_str());
     int connectCounter = 0;
     bool successful = true;
@@ -29,7 +30,7 @@ void WifiManager::startWifi()
 
     while (WiFi.status() != WL_CONNECTED)
     {
-      Serial.printf("WiFI connection problem %d\n", WiFi.status());
+      LOG_INFO("WiFI connection problem %d", WiFi.status());
       WiFi.begin(staSSID.c_str(), staPassword.c_str());
 
       connectCounter += 1;
@@ -51,13 +52,13 @@ void WifiManager::startWifi()
 
   if (apPassword.length() > 0)
   {
-    Serial.printf("Secured AP mode, name %s\n", wifiStaModeName_.c_str());
+    LOG_INFO("Secured AP mode, name %s\n", wifiStaModeName_.c_str());
     WiFi.softAP(wifiStaModeName_.c_str(), apPassword.c_str());
     state_ = AP_SECURE;
   }
   else
   {
-    Serial.printf("Provisioning AP mode, name %s\n", wifiStaModeName_.c_str());
+    LOG_INFO("Provisioning AP mode, name %s\n", wifiStaModeName_.c_str());
     WiFi.softAP(wifiStaModeName_.c_str());
     state_ = AP_PROVISIONING;
   }
@@ -92,7 +93,7 @@ void WifiManager::iteration()
   if (state_ == STA && WiFi.status() != WL_CONNECTED)
   {
     startWifi();
-    Serial.println("Connection lost - Restarting WIFI");
+    LOG_WARNING("Connection lost - Restarting WIFI");
   }
 }
 
diff --git a/firmware/src/SessionAPI.h b/firmware/src/SessionAPI.h
index ab32caf..0f9ef9b 100644
--- a/firmware/src/SessionAPI.h
+++ b/firmware/src/SessionAPI.h
@@ -86,11 +86,11 @@ bool SessionAPI<T>::handleMessage(websockets::WebsocketsClient &client, MessageC
   switch (code)
   {
   case MessageCode::START_SESSION:
-    Serial.println("SessionAPI: starting measurement session");
+    LOG_INFO("SessionAPI: starting measurement session");
     this->sessionManager_.startMeasurements();
     return true;
   case MessageCode::STOP_SESSION:
-    Serial.println("SessionAPI: stopping measurement session");
+    LOG_INFO("SessionAPI: stopping measurement session");
     this->sessionManager_.stopMeasurements();
     return true;
   case MessageCode::TARE:
diff --git a/firmware/src/WebsocketServer.h b/firmware/src/WebsocketServer.h
index 3244d6a..f7e69ce 100644
--- a/firmware/src/WebsocketServer.h
+++ b/firmware/src/WebsocketServer.h
@@ -48,15 +48,14 @@ public:
 
     if (server_.poll())
     {
-      Serial.printf("new websocket connection, storing at pos %d - occupancy: ", nextFreeClient_);
+      LOG_INFO("new websocket connection, storing at pos %d - occupancy: ", nextFreeClient_);
       clients_[nextFreeClient_] = server_.accept();
       clients_[nextFreeClient_].onMessage(onMessage);
       this->onClientConnectImpl(clients_[nextFreeClient_]);
       nextFreeClient_ = (nextFreeClient_ + 1) % MAX_WEBSOCKET_CONNECTIONS;
 
       for (int i = 0; i < MAX_WEBSOCKET_CONNECTIONS; ++i)
-        Serial.print((clients_[i].available()) ? "x" : "o");
-      Serial.print("\n");
+        LOG_INFO((clients_[i].available()) ? "x" : "o");
     }
 
     for (int i = 0; i < MAX_WEBSOCKET_CONNECTIONS; ++i)
diff --git a/firmware/src/WifiAPI.cpp b/firmware/src/WifiAPI.cpp
index 1f778d2..1f639e9 100644
--- a/firmware/src/WifiAPI.cpp
+++ b/firmware/src/WifiAPI.cpp
@@ -35,21 +35,21 @@ bool WifiAPI::handleMessage(websockets::WebsocketsClient &client, MessageCode co
     }
     if (json.containsKey("reset_to_provisioning") && json["reset_to_provisioning"].as<bool>())
     {
-      Serial.println("wifi: reset_to_provisioning");
+      LOG_INFO("wifi: reset_to_provisioning");
       wifiManager_.resetToApProvisioning();
       restartScheduled_ = true;
       return true;
     }
     else if (json.containsKey("ap_password"))
     {
-      Serial.println("wifi: ap_password");
+      LOG_INFO("wifi: ap_password");
       wifiManager_.setApCredentials(json["ap_password"].as<const char *>());
       restartScheduled_ = true;
       return true;
     }
     else if (json.containsKey("sta_ssid") && json.containsKey("sta_password"))
     {
-      Serial.println("wifi: sta_ssid");
+      LOG_INFO("wifi: sta_ssid");
       wifiManager_.setStaCredentials(json["sta_ssid"].as<const char *>(), //
                                      json["sta_password"].as<const char *>());
       restartScheduled_ = true;
diff --git a/firmware/src/WifiAPI.h b/firmware/src/WifiAPI.h
index eafd30b..b7437b6 100644
--- a/firmware/src/WifiAPI.h
+++ b/firmware/src/WifiAPI.h
@@ -36,7 +36,7 @@ void WifiAPI::iteration(TServer &server)
 {
   if (restartScheduled_)
   {
-    Serial.print("Restart triggered by WifiAPI");
+    LOG_INFO("Restart triggered by WifiAPI");
     ESP.restart();
   }
   reportScanResultIfAvailable(server);
diff --git a/firmware/src/firmware_main.cpp b/firmware/src/firmware_main.cpp
index 8147084..d68a0f7 100644
--- a/firmware/src/firmware_main.cpp
+++ b/firmware/src/firmware_main.cpp
@@ -14,19 +14,20 @@
 #include "WifiManager.h"
 #include "MockScale.h"
 #include "Scale.h"
-#include "MeasurementSession.h"
 #include "SessionManager.h"
-#include "SpiffsStorage.h"
 #include "SimpleMeasurementSession.h"
 #include "EspHttp.h"
 #include "WebDAV.h"
 #include "UserDB.h"
+#include "Logger.h"
+
 
 // Api
 #include "WebsocketServer.h"
 #include "SessionAPI.h"
 #include "WifiAPI.h"
 
+
 using Session_T = SimpleMeasurementSession<MeasurementT, CONFIG_SESSION_MAX_SIZE>;
 SessionManager<Session_T> sessionManager;
 
@@ -55,20 +56,19 @@ String getIdSuffix()
 bool firmwareUpdate()
 {
     esp_http_client_config_t config;
-    Serial.println((char *)certificate_pem);
     memset(&config, 0, sizeof(esp_http_client_config_t));
     config.url = UPDATE_URL;
     config.cert_pem = (char *)certificate_pem;
-    Serial.println("Starting firmware upgrade");
+    LOG_INFO("Starting firmware upgrade");
     esp_err_t ret = esp_https_ota(&config);
     if (ret == ESP_OK)
     {
-        Serial.println("Firmware upgrade successful - restarting");
+        LOG_INFO("Firmware upgrade successful - restarting");
         esp_restart();
     }
     else
     {
-        Serial.println("Firmware upgrade failed");
+        LOG_WARNING("Firmware upgrade failed");
         return false;
     }
     return true;
@@ -108,23 +108,23 @@ void httpSetup(SessionManager<SessionT> *sessionManager, WifiManager *wifiManage
         httpd_resp_set_hdr(req, "Access-Control-Allow-Origin", "*");
         httpd_resp_send(req, "Session started", -1);
         sessionManager->startMeasurements();
-        Serial.println("Started session");
+        LOG_INFO("RestAPI: Started session");
     };
     auto cbStopSession = [sessionManager](httpd_req_t *req)
     {
         httpd_resp_set_hdr(req, "Access-Control-Allow-Origin", "*");
         httpd_resp_send(req, "Session stopped", -1);
         sessionManager->stopMeasurements();
-        Serial.println("Stopped session");
+        LOG_INFO("RestAPI: Stopped session");
     };
     auto cbRestart = [](httpd_req_t *req)
     {
-        Serial.println("Restarted requested");
+        LOG_INFO("RestAPI: Restarted requested");
         ESP.restart();
     };
     auto cbTare = [sessionManager](httpd_req_t *req)
     {
-        Serial.println("Tare");
+        LOG_INFO("RestAPI: Tare");
         sessionManager->tare();
     };
     auto cbFirmwareUpdate = [](httpd_req_t *req)
@@ -409,11 +409,11 @@ void httpSetup(SessionManager<SessionT> *sessionManager, WifiManager *wifiManage
         espHttpServer.on("/webdav/*?", HTTP_PROPFIND, webdav);
         espHttpServer.on("/webdav/*?", HTTP_DELETE, webdav);
         espHttpServer.on("/webdav/*?", HTTP_OPTIONS, webdav);
-        Serial.println("HTTP setup done");
+        LOG_INFO("HTTP setup done");
     }
     else
     {
-        Serial.println("HTTP setup with limited API in provisioning mode");
+        LOG_INFO("HTTP setup with limited API in provisioning mode");
     }
 }
 
@@ -421,49 +421,47 @@ void mdnsSetup(const String &fullHostname)
 {
     if (!MDNS.begin(fullHostname.c_str()))
     {
-        Serial.println("Error setting up MDNS responder!");
+        LOG_INFO("Error setting up MDNS responder!");
         while (true)
         {
             delay(1000);
         }
     }
-    Serial.printf("mDNS started %s\n", fullHostname.c_str());
+    LOG_INFO("mDNS started %s", fullHostname.c_str());
     MDNS.addService("swimtracker", "tcp", 81);
 }
 
 void setup()
 {
     // Serial
-    Serial.begin(115200);
-    while (!Serial)
-    {
-    }
+    Logger::init();
 
     // File system
     auto millisBeforeSpiffsInit = millis();
     bool spiffsResult = SPIFFS.begin(true);
     if (!spiffsResult)
-        Serial.println("Failed to mount/format SPIFFS file system");
+        LOG_WARNING("Failed to mount/format SPIFFS file system");
 
     ESP_ERROR_CHECK(esp_event_loop_create_default());
     
     auto spiffsSetupTimeSecs = (millis() - millisBeforeSpiffsInit) / 1000;
 
     userStorage.init();
-    Serial.printf("Spiffs size: %d MB, setup time %d secs\n", portablefs::totalBytes() / 1024 / 1024, spiffsSetupTimeSecs);
+    LOG_INFO("Spiffs size: %d MB, setup time %ld secs", portablefs::totalBytes() / 1024 / 1024, spiffsSetupTimeSecs);
 
     // WiFi
     Preferences prefs;
     String uniqueName = "swimtracker" + getIdSuffix();
     String configuredHostname = prefs.getString("hostname", CONFIG_HOSTNAME + getIdSuffix());
     wifiManager.begin(configuredHostname, uniqueName);
-    Serial.print("Connected to WiFi. IP:");
-    Serial.println(WiFi.localIP());
-    Serial.printf("WIFI state: %s\n", wifiManager.stateStr());
+    const auto ip = WiFi.localIP();
+    LOG_INFO("Connected to WiFi. IP: %u.%u.%u.%u", ip[0], ip[1], ip[2], ip[3]);
+    LOG_INFO("WIFI state: %s", wifiManager.stateStr());
 
     mdnsSetup(configuredHostname);
 
     sessionManagerSetup();
+    Logger::setNtpTime(sessionManager.getNtpTime());
     sessionManager.tare();
 
     // HTTP & Websocket server