Originally Posted by Erhard

Very very clear rule is 4.20V as you see on the pictures taken from the event (Thanks to https://www.rctech.net/forum/showpos...ostcount=48147)
and certainly easy to understand for driver and team already during qualifying.

Rules of rounding numbers is that 4.20499999999 is 4.20 and 4.2050000000000 etc. is 4.21.
Voltage meters of medium price are good for 1/1000Volts accuracy. So you just have to make sure to be below 4.204.