diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 3a84a22..78a82f6 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -9,4 +9,4 @@ build:
   script:
     - cd firmware
     - platformio run
-    #- platformio test -v -e native
+    - platformio test -v -e native
diff --git a/firmware/dat/.dont_remove b/firmware/dat/.dont_remove
new file mode 100644
index 0000000..e69de29
diff --git a/firmware/lib/basic/Dtypes.h b/firmware/lib/basic/Dtypes.h
index 3fd8b21..5d83f8f 100644
--- a/firmware/lib/basic/Dtypes.h
+++ b/firmware/lib/basic/Dtypes.h
@@ -1,6 +1,12 @@
 #pragma once
 
-inline void _assert(const char* expression, const char* message, const char* file, int line)
+#ifndef PLATFORM_NATIVE
+
+// ---------------------------------- Arduino -------------------------------------------------------------
+
+#include <Arduino.h>
+
+inline void _assert(const char *expression, const char *message, const char *file, int line)
 {
     Serial.print("Assert ");
     Serial.print(file);
@@ -12,9 +18,58 @@ inline void _assert(const char* expression, const char* message, const char* fil
     Serial.println(message);
 }
 
-template< typename T>
-inline String toString(const T & t) {
+template <typename T>
+inline String toString(const T &t)
+{
     return String(t);
 }
 
 #define assert_msg(EXPRESSION, MSG) ((EXPRESSION) ? (void)0 : _assert(#EXPRESSION, #MSG, __FILE__, __LINE__))
+
+#else
+// ---------------------------------- Native -----------------------------------------------------------------
+
+#include <string>
+#include <cstdint>
+#include <cstring>
+#include <arpa/inet.h>
+#include <algorithm>
+#include <iostream>
+#include <sstream>
+#include <string>
+
+typedef uint32_t uint_t;
+
+typedef std::string String;
+typedef uint8_t byte;
+typedef const char *PGM_P;
+
+using std::max;
+using std::min;
+
+inline uint32_t strlen_P(PGM_P str)
+{
+    return std::strlen(str);
+}
+
+inline const char *F(const char *in) { return in; }
+
+inline void _assert(const char *expression, const char *message, const char *file, int line)
+{
+    std::cerr << "Assert " << file << ":" << line << "  '" << expression << "' failed." << std::endl;
+    std::cerr << message << std::endl;
+
+    abort();
+}
+
+template <typename T>
+inline std::string toString(const T &t)
+{
+    std::stringstream stream;
+    stream << t;
+    return stream.str();
+}
+
+#define assert_msg(EXPRESSION, MSG) ((EXPRESSION) ? (void)0 : _assert(#EXPRESSION, #MSG, __FILE__, __LINE__))
+
+#endif
\ No newline at end of file
diff --git a/firmware/lib/basic/FilesystemAbstraction.h b/firmware/lib/basic/FilesystemAbstraction.h
index e89b898..790f5b8 100644
--- a/firmware/lib/basic/FilesystemAbstraction.h
+++ b/firmware/lib/basic/FilesystemAbstraction.h
@@ -1,5 +1,7 @@
 #pragma once
 
+#include "Dtypes.h"
+
 #ifdef PLATFORM_ESP32
 #include "SPIFFS.h"
 
@@ -93,7 +95,6 @@ namespace portablefs
 #include <string>
 #include <fstream>
 #include <filesystem>
-#include "MockDtypes.h"
 
 namespace fs = std::filesystem;
 
diff --git a/firmware/lib/basic/MockDtypes.h b/firmware/lib/basic/MockDtypes.h
deleted file mode 100644
index 857d1e1..0000000
--- a/firmware/lib/basic/MockDtypes.h
+++ /dev/null
@@ -1,46 +0,0 @@
-#pragma once
-
-#include <string>
-#include <cstdint>
-#include <cstring>
-#include <arpa/inet.h>
-#include <algorithm>
-#include <iostream>
-#include <sstream>
-#include <string>
-
-typedef uint32_t uint_t;
-
-typedef std::string String;
-typedef uint8_t byte;
-typedef const char * PGM_P;
-
-using std::min;
-using std::max;
-
-inline uint32_t strlen_P(PGM_P str) {
-    return std::strlen(str);
-}
-
-inline const char * F( const char * in) { return in; }
-
-
-inline void _assert(const char* expression, const char* message, const char* file, int line)
-{
-    std::cerr << "Assert " << file << ":" << line << "  '" << expression << "' failed." << std::endl;
-    std::cerr << message << std::endl;
-
-    abort();
-}
-
-template< typename T>
-inline std::string toString(const T & t) {
-    std::stringstream stream;
-    stream << t;
-    return stream.str();
-}
-
-class String : public std::string
-{};
-
-#define assert(EXPRESSION, MSG) ((EXPRESSION) ? (void)0 : _assert(#EXPRESSION, #MSG, __FILE__, __LINE__))
\ No newline at end of file
diff --git a/firmware/lib/scale/Scale.h b/firmware/lib/scale/Scale.h
index 109723e..55748d7 100644
--- a/firmware/lib/scale/Scale.h
+++ b/firmware/lib/scale/Scale.h
@@ -11,8 +11,8 @@ public:
         if (hx711_.is_ready())
         {
             long value = hx711_.read_average(CONFIG_MEASUREMENT_AVG_COUNT) - offset_;
-            if(value > 0)
-                measurementOut = (int16_t)(value / DIVIDER);
+            if(value < 0)
+                measurementOut = (int16_t)(-value / DIVIDER);
             else
                 measurementOut = 0;
             return true;
diff --git a/firmware/lib/session/MeasurementSession.h b/firmware/lib/session/MeasurementSession.h
index ef99e1b..a28e38b 100644
--- a/firmware/lib/session/MeasurementSession.h
+++ b/firmware/lib/session/MeasurementSession.h
@@ -126,7 +126,7 @@ private:
     }
 
     static String chunkFileName(uint32_t chunkNr, uint32_t startTime) {
-        return("/dat/" + toString(startTime) + "_" + toString(chunkNr));
+        return("/dat/" + toString(startTime) + String("_") + toString(chunkNr));
     }
 
     Chunk_T chunks[2];
diff --git a/firmware/lib/userdb/UserDB.h b/firmware/lib/userdb/UserDB.h
index cd866d9..30b5247 100644
--- a/firmware/lib/userdb/UserDB.h
+++ b/firmware/lib/userdb/UserDB.h
@@ -1,9 +1,6 @@
 #pragma once
 
-#ifndef PLATFORM_NATIVE
-#include <Arduino.h>
-#endif
-
+#include "Dtypes.h"
 
 using SessionIdType = uint32_t;
 constexpr size_t MAX_USERS = 64;
diff --git a/firmware/lib/webdav/AsyncWebDav.h b/firmware/lib/webdav/AsyncWebDav.h
index e2a9e5a..a45fbd4 100644
--- a/firmware/lib/webdav/AsyncWebDav.h
+++ b/firmware/lib/webdav/AsyncWebDav.h
@@ -41,8 +41,7 @@ public:
 
     size_t operator()(uint8_t *buffer, size_t maxLen, size_t index)
     {
-        Serial.print("index ");
-        Serial.println(index);
+        Serial.printf("%ld index %u\n", millis(), index);
 
         using namespace webdav_constants;
         uint8_t *bufferStart = buffer;
@@ -57,6 +56,7 @@ public:
         }
 
         bool fileFound = false;
+        Serial.printf("%ld (0)\n", millis());
         while (dir_.next())
         {
             if (isFirstFileOfTrainingGroup())
@@ -71,10 +71,12 @@ public:
             //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);
@@ -89,9 +91,11 @@ public:
             {
                 toBuffer(buffer, CONTENTLEN_START);
                 String fileSizeStr(getFileSize(fileName));
-                toBuffer(buffer, fileSizeStr.c_str());
+                //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);
@@ -104,10 +108,10 @@ public:
             finished_ = true;
         }
 
+
         size_t bytesWritten = buffer - bufferStart;
         assert_msg(bytesWritten < maxLen, "Written too much!");
-        //Serial.print("Bytes written ");
-        //Serial.println(bytesWritten);
+        Serial.printf("%ld Bytes written %u\n", millis(), bytesWritten);
         //Serial.print("Max bytes ");
         //Serial.println(maxLen);
         return bytesWritten;
diff --git a/firmware/src/ConfigHardware.h b/firmware/src/ConfigHardware.h
index ff6978f..c32eda7 100644
--- a/firmware/src/ConfigHardware.h
+++ b/firmware/src/ConfigHardware.h
@@ -3,10 +3,10 @@
 #include <cstdint>
 
 
-//#define _HW_V_20
+#define _HW_V_20
 
 // HX711 load cell
-#ifdef USE_ESP32
+#ifdef PLATFORM_ESP32
 
 #ifdef  _HW_V_20
 const int CONFIG_SCALE_DOUT_PIN = 23;
@@ -20,10 +20,10 @@ const int CONFIG_SCALE_SCK_PIN = 23;
 const int CONFIG_SCALE_DOUT_PIN = D2;
 const int CONFIG_SCALE_SCK_PIN = D3;
 #endif
-const uint8_t CONFIG_MEASUREMENT_AVG_COUNT = 1; // number of measurements in normal phase
-const uint8_t CONFIG_TARE_AVG_COUNT = 6;        // number of measurements in tare-phase (to find 0 )
-const int CONFIG_MEASURE_DELAY = 100;           // interval in ms between measurements
+const uint8_t CONFIG_MEASUREMENT_AVG_COUNT = 1;  // number of measurements in normal phase
+const uint8_t CONFIG_TARE_AVG_COUNT = 6;         // number of measurements in tare-phase (to find 0 )
+const int CONFIG_MEASURE_DELAY = 100;            // interval in ms between measurements
 //const int CONFIG_VALUE_DIVIDER = 8;             // uint32 measurements are divided by this factor, before stored in uint16_t
-const int CONFIG_VALUE_DIVIDER = 256;             // uint32 measurements are divided by this factor, before stored in uint16_t
+const int CONFIG_VALUE_DIVIDER = 128;             // uint32 measurements are divided by this factor, before stored in uint16_t
 
 const uint32_t CONFIG_SESSION_CHUNK_SIZE = 1024; //1024*8 - 16 * sizeof(uint32_t);
diff --git a/firmware/src/firmware_main.cpp b/firmware/src/firmware_main.cpp
index 1081287..ef25943 100644
--- a/firmware/src/firmware_main.cpp
+++ b/firmware/src/firmware_main.cpp
@@ -1,8 +1,8 @@
-#define USE_ESP32
 
 // Arduino & ESP headers
-#include <Arduino.h>
-#ifdef USE_ESP32
+#include "Dtypes.h"
+
+#ifdef PLATFORM_ESP32
 #include <WiFi.h>
 #else
 #include <ESP8266WiFi.h>
@@ -13,7 +13,6 @@
 #include <NTPClient.h> // for NTP
 
 // Own libs
-#include "Dtypes.h"
 #include "MockScale.h"
 #include "Scale.h"
 #include "MeasurementSession.h"
@@ -207,7 +206,7 @@ void setup()
     // WiFi
     WiFi.mode(WIFI_STA);
     WiFi.begin(CONFIG_WIFI_SSID, CONFIG_WIFI_PASSWORD);
-    #ifdef USE_ESP32
+    #ifdef PLATFORM_ESP32
     WiFi.setHostname(CONFIG_HOSTNAME);
     #else
     WIFI.hostname(CONFIG_HOSTNAME);
@@ -232,6 +231,10 @@ void setup()
 
     Serial.println("Spiffs listing:");
     listDir(SPIFFS, "/", 3);
+
+    // 
+    Serial.print("Free Heap");
+    Serial.println(ESP.getFreeHeap());
 }
 
 void loop() {
diff --git a/firmware/test/test_common/sessiontest.cpp b/firmware/test/test_common/sessiontest.cpp
index bfceac3..6ea066e 100644
--- a/firmware/test/test_common/sessiontest.cpp
+++ b/firmware/test/test_common/sessiontest.cpp
@@ -1,4 +1,4 @@
-#include "MockDtypes.h"
+#include "Dtypes.h"
 #include "MockSerial.h"
 #include "MeasurementSession.h"
 #include "MockStorage.h"
diff --git a/hardware/calibration.txt b/hardware/calibration.txt
new file mode 100644
index 0000000..ed30f93
--- /dev/null
+++ b/hardware/calibration.txt
@@ -0,0 +1,6 @@
+Old load cell 
+    const int CONFIG_VALUE_DIVIDER = 128;
+    1kg ~= 700
+    => overflow at 93 kg
+
+