diff --git a/README.md b/README.md
index c32d4ea..9117dc2 100644
--- a/README.md
+++ b/README.md
@@ -1,27 +1,63 @@
 # XCTRACK_vario DO IT YOURSELF !
-Variometer for XCTRACK (https://xctrack.org/) base on ms5611 high precision pressure and temperature sensor and LK8000
 
-It's works with USB or Bluetooth on XCtrack !
+## Table of Contents
 
-Power consumption ~ 0.1W ( a little bit more with bluetooth )
+- [Overview](#overview)
+- [Components](#components)
+- [Step by step](#step-by-step)
+- [Diagrams](#diagrams)
+    * [USB support only](#usb-support-only)
+    * [USB and bluetooth support](#usb-and-bluetooth-support)
+- [Known issues](#known-issues)
+  
+## Overview 
+
+Variometer for [XCTRACK](https://xctrack.org/) based on MS5611 high precision pressure and temperature sensor and LK8000.
+
+It works via USB or Bluetooth on XCtrack!
+
+Power consumption ~0.1W (a little bit more with bluetooth)
 
 Based on Arduino Vario by Benjamin PERRIN 2017 / Vari'Up
 Based on Arduino Vario by Jaros, 2012 and vario DFelix 2013
 https://github.com/LK8000/LK8000/blob/master/Docs/LK8EX1.txt
 
-parts :
-- arduino nano with ftdi chip ( or ch340g chip since xctrack 0.9.3)
-- ms5611 pressure and temperature sensor
-- bluetooth module in option ( hc-05 or hc-06 or cpp module )
-- usb mini - micro - type c OTG cable (if USB mode) , depends on your phone 
+### Components
+- Arduino Nano with FTDI chip (or ch340g chip since xctrack 0.9.3)
+- MS5611 pressure and temperature sensor
+- bluetooth module in option (hc-05 or hc-06 or cpp module (ZS-040))
+- USB mini/micro/type c OTG cable (if USB mode), depends on your phone
 <a href="https://my.aliexpress.com/wishlist/shared.htm?groupId=100000009108834" target="_blank">aliexpress</a>
-
 - PLA box 3D printing
 <a href="https://cad.onshape.com/documents/8ec970df0f91cd7f4dafb0b8/w/81f5e80ab2d84901aa8e29be/e/2df0103f0eb100d6330b3609" target="_blank">Onshape</a>
-
+  
 ![alt text](img/xctrack512.jpg)
 
-## with usb support only
+## Step by step
+
+1) Download MS5XXX library by Roman Schmitz. (Go to Tools, Manage Libraries and search for "MS5xxx"; install the library done by  Roman Schmitz.)
+
+1) If you want to use it as only usb, just upload the code in (XCTRACK_VARIO_MS5611/XCTRACK_VARIO_MS5611.ino).
+
+To use it as bluetooth (and USB), simply change the following code
+
+```
+#define USB_MODE // usb by default
+// #define BLUETOOTH_MODE // uncomment this line for bluetooth mode
+```
+
+to
+
+```
+#define USB_MODE // usb by default
+#define BLUETOOTH_MODE // uncomment this line for bluetooth mode
+```
+
+Note: To build this vario, you *may* be able to use other Arduinos besides the nano: simply connect the SCL/SDA of the MS5611 to the respective SCL/SDA ports of your Arduino.
+
+## Diagrams
+
+### USB support only
 
 ![alt text](img/vario_MS5611.png)
 
@@ -29,8 +65,33 @@ parts :
 
 ![alt text](img/usb-c_soldered.jpg)
 
-## with usb and bluetooth support
+### USB and bluetooth support
 
 ![alt text](img/vario_MS5611_bluetooth.png)
 
 ![alt text](img/usb-mini_bluetooth_soldered.jpg)
+
+
+### Known issues
+
+#### The arduino seems bricked
+You may have connected the SCL/SDA ports wrong. 
+
+If you can't upload to your arduino:
+
+1) Disconnect it from the computer 
+   
+1) Press and hold the reset button
+
+1) Plug it back (don't release the reset)
+   
+1) Click upload (don't release the reset)
+   
+1) When the IDE says that is uploading (after compiling ends) release the reset button
+
+#### Can't upload
+Assuming you are using a nano, you may have an older bootloader version. 
+
+Change the processor to "ATmega328P (Old Bootloader)" 
+
+![img.png](img/old-bootloader.png)
\ No newline at end of file
diff --git a/XCTRACK_VARIO_MS5611/XCTRACK_VARIO_MS5611.ino b/XCTRACK_VARIO_MS5611/XCTRACK_VARIO_MS5611.ino
index 750570e..4c67505 100644
--- a/XCTRACK_VARIO_MS5611/XCTRACK_VARIO_MS5611.ino
+++ b/XCTRACK_VARIO_MS5611/XCTRACK_VARIO_MS5611.ino
@@ -27,8 +27,8 @@ SoftwareSerial BTserial(RX, TX); // RX not connected
 #define USB_SPEED 115200 //serial transmision speed
 #define BLUETOOTH_SPEED 9600 //bluetooth speed (9600 by default)
 #define FREQUENCY 10 // freq output in Hz
-#define USB_MODE // uncomment for usb mode
-#define BLUETOOTH_MODE // uncomment for bluetooth mode
+#define USB_MODE // usb by default
+// #define BLUETOOTH_MODE // uncomment this line for bluetooth mode
 #define USE_LK8000
 /*
  * sentences to choice : 
diff --git a/img/old-bootloader.png b/img/old-bootloader.png
new file mode 100644
index 0000000..2280646
Binary files /dev/null and b/img/old-bootloader.png differ