README.md update

README.md

@@ -39,3 +39,15 @@ By default CHIRP shows only default channel options, that are universal for all
 
 This driver supports custom Egzumer firmware builds and detects which [options](https://github.com/egzumer/uv-k5-firmware-custom?tab=readme-ov-file#user-customization) have been used.
 Disabled options will be hidden in CHIRP. This only works if the configuration was read from a specific radio. You can use configuration files from other radios with different build options, but unsupported settings will be reset to defaults on the target radio.
+
+# Calibration settings
+
+Those setting are not uploaded to the radio by default. If you make some changes in the calibration and you want to save it, you have to enable the `Upload calibration` option before uploading. If this is enabled only the calibration part of the configuration data is sent to the radio, without channels and other settings. 
+
+Use this option at your own risk. Make a backup of the calibration first! Some settings are calibrated at the factory and each radio has different and unique calibration data. You will not be able to restore those setting using some other radios settings. Be carefull not to use CHIRP config file that was downloaded from other radio. Each CHIRP config contains full EEPROM dump, it always did, even the original UV-K5 driver did this, so if you have some old config saved it also contains calibration section and can be used to restore the calibration, but the best way to make a backup is to use software that doesn't depend on CHIRP driver, like [k5prog-win](https://github.com/OneOfEleven/k5prog-win/raw/main/k5prog_win.exe).
+
+Calibration settings are raw values read from the EEPROM, not recalculated to dBm, dB or any particular units. All the settings are presented as they were in the stock Quansheng firmware. Not all calibration settings are used the same way by the egzumer firmware:
+- Squelch - sensitivity is doubled if ENABLE_SQUELCH_MORE_SENSITIVE is enabled (enabled by default)
+- Microphone sensitivity - not used at all
+- RSSI levels - only used for small RSSI bar indicator if the firmware is built with the custom S-meter disabled (ENABLE_RSSI_BAR = 0)
+- TX power - if built with ENABLE_REDUCE_LOW_MID_TX_POWER then medium power is further divided by 3, low power is divided by 5 (not enabled by default)