diff --git a/README.md b/README.md
index 44ff01e..2f2b964 100644
--- a/README.md
+++ b/README.md
@@ -8,81 +8,132 @@ NanoVNA - Very tiny handheld Vector Network Analyzer
 
 # About
 
-NanoVNA is very tiny handheld Vector Network Analyzer (VNA). It is
-standalone with lcd display, portable device with battery. This
-project aim to provide an RF gadget but useful instrument for
-enthusiast.
+**NanoVNA-H** and **NanoVNA-H4** are very tiny handheld Vector Network Analyzers (VNA).
+They are standalone portable devices withLCD and battery.
+This project aims to provide improved firmware for this useful instrument for enthusiast.
 
-This repository contains source of NanoVNA firmware.
+This repository contains the source code of the improved NanoVNA-H and NanoVNA-H4 firmware.
+
+The documentation describes the build and flash process on a MacOS or a Linux (Debian or Ubuntu) system, other Linux (or even BSD) systems may behave similar.
 
 ## Prepare ARM Cross Tools
 
-**UPDATE**: Recent gcc version works to build NanoVNA, no need old version.
+**UPDATE**: Recent gcc version works to build NanoVNA, no need to use old version.
 
 ### MacOSX
 
 Install cross tools and firmware updating tool.
 
-    $ brew tap px4/px4
-    $ brew install gcc-arm-none-eabi-80
-    $ brew install dfu-util
+    brew tap px4/px4
+    brew install gcc-arm-none-eabi-80
+    brew install dfu-util
 
 ### Linux (ubuntu)
 
 Download arm cross tools from [here](https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm/downloads).
 
-    $ wget https://developer.arm.com/-/media/Files/downloads/gnu-rm/8-2018q4/gcc-arm-none-eabi-8-2018-q4-major-linux.tar.bz2
-    $ sudo tar xfj gcc-arm-none-eabi-8-2018-q4-major-linux.tar.bz2 -C /usr/local
-    $ PATH=/usr/local/gcc-arm-none-eabi-8-2018-q4-major/bin:$PATH
-    $ sudo apt install -y dfu-util
+    wget https://developer.arm.com/-/media/Files/downloads/gnu-rm/8-2018q4/gcc-arm-none-eabi-8-2018-q4-major-linux.tar.bz2
+    sudo tar xfj gcc-arm-none-eabi-8-2018-q4-major-linux.tar.bz2 -C /usr/local
+    PATH=/usr/local/gcc-arm-none-eabi-8-2018-q4-major/bin:$PATH
+    sudo apt install -y dfu-util
+
 ### Debian
-    $ sudo apt install gcc-arm-none-eabi
-    $ sudo apt install -y dfu-util
 
-## Fetch source code
+    sudo apt install gcc-arm-none-eabi
+    sudo apt install -y dfu-util
+
+## Fetch Source Code
+
+Fetch the firmware source and the submodule, do this once to initialize your local clone from GitHub:
+
+    git clone https://github.com/DiSlord/NanoVNA-D.git
+    cd NanoVNA-D
+    git submodule update --init --recursive
+
+## Update Source Code
+
+To get updates from the GitHub repository, go to your `NanoVNA-D` directory and type:
+
+    git pull
+
+## Build the NanoVNA-H Firmware
+
+Go to your `NanoVNA-D` directory and type:
+
+    export TARGET=F072
+    make clean
+    make
+
+## Build the NanoVNA-H4 Firmware
+
+Go to your `NanoVNA-D` directory and type:
+
+    export TARGET=F303
+    make clean
+    make
+
+## Flash Firmware
+
+When the build of your firmware is finished, you can flash it onto your NanoVNA device.
+First, let the device enter DFU mode by one of following methods.
+
+* Open the device and jumper `BOOT0` pin to `Vdd` pin when powering the device.
+* Select menu Config->DFU (needs recent firmware).
+* Press the jog switch on your -H4 when powering the device.
+
+Then, flash the firmware using `dfu-util` via USB.
 
-Fetch source and submodule.
+#### For NanoVNA-H:
 
-    $ git clone https://github.com/DiSlord/NanoVNA-D.git
-    $ cd NanoVNA
-    $ git submodule update --init --recursive
+Go to your `NanoVNA-D` directory and type:
 
-## Build
+    dfu-util -d 0483:df11 -a 0 -s 0x08000000:leave -D build/H.bin
 
-Just make in the directory.
+#### For NanoVNA-H4:
 
-    $ make
+Go to your `NanoVNA-D` directory and type:
 
-## Flash firmware
+    dfu-util -d 0483:df11 -a 0 -s 0x08000000:leave -D build/H4.bin
 
-First, make device enter DFU mode by one of following methods.
+#### Or simply type directly after building the firmware (for both variants).
 
-* Jumper BOOT0 pin at powering device
-* Select menu Config->DFU (needs recent firmware)
+Go to your `NanoVNA-D` directory and type:
 
-Then, flash firmware using dfu-util via USB.
+    make flash
 
-    $ dfu-util -d 0483:df11 -a 0 -s 0x08000000:leave -D build/ch.bin
+#### Ignore the apparent error message during flashing
 
-Or simply use make.
+The low-level tool `dfu-util` displays a lot of information that is very useful especially for developers, but can confuse the user.
+In particular, please ignore the message about corrupt firmware, this is the normal behaviour of the unit before clearing the status.
+It is important to note that after clearing the status, there is no longer an error condition present.
 
-    $ make flash
+```
+...
+Determining device status...
+DFU state(10) = dfuERROR, status(10) = Device's firmware is corrupt. It cannot return to run-time (non-DFU) operations
+Clearing status
+Determining device status...
+DFU state(2) = dfuIDLE, status(0) = No error condition is present
+...
+```
 
 ## Companion Tools
 
-There are seveal numbers of great companion PC tools from third-party.
+There are several numbers of great companion PC tools from third-party.
 
 * [NanoVNA-App software](https://github.com/OneOfEleven/NanoVNA-H/blob/master/Release/NanoVNA-App.rar) by OneOfEleven
 * [NanoVNASharp Windows software](https://drive.google.com/drive/folders/1IZEtx2YdqchaTO8Aa9QbhQ8g_Pr5iNhr) by hugen79
 * [NanoVNA WebSerial/WebUSB](https://github.com/cho45/NanoVNA-WebUSB-Client) by cho45
 * [Android NanoVNA app](https://play.google.com/store/apps/details?id=net.lowreal.nanovnawebapp) by cho45
-* [NanoVNASaver](https://github.com/mihtjel/nanovna-saver) by mihtjel
+* [NanoVNASaver](https://github.com/NanoVNA-Saver/nanovna-saver) by mihtjel and the members of NanoVNA-Saver
 * [TAPR VNAR4](https://groups.io/g/nanovna-users/files/NanoVNA%20PC%20Software/TAPR%20VNA) supports NanoVNA by erikkaashoek
+* [The NanoVNA toolbox](https://github.com/Ho-Ro/nanovna-tools) by Ho-Ro
 * see [python](/python/README.md) directory to use NanoVNA with Python and Jupyter Notebook.
 
 ## Documentation
 
 * [NanoVNA User Guide(ja)](https://cho45.github.io/NanoVNA-manual/) by cho45. [(en:google translate)](https://translate.google.com/translate?sl=ja&tl=en&u=https%3A%2F%2Fcho45.github.io%2FNanoVNA-manual%2F)
+* [NanoVNA user group](https://groups.io/g/nanovna-users/topics) on groups.io.
 
 ## Reference