I just got a Nano Every and found that the value read by ADC is inaccurate. So I disconnect everything except USB. After measuring I found that I can only get 4.5~4.7v from 5V pin. The voltage of 3V3 pin is correct. Changing power source from pc to a power bank or a 5V2A charger didn't solve it. Is this normal?
For now I have to use another ADC channel to measure 3V3 pin and do some math to get the correct value from ADC. 
Yes it is normal. Nothing to worry about. It applies to all micro controllers not just the Nano.
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You can do that of cource but you still will not be able to measure voltages greater than the voltage you measure on the 5V pin. If it's 4.5V than your ADC range will be 0 to 4.5V.
Plus that voltage is not stable and will vary. So you need to do a calibration before each measurement.
If the Every is like the classic Nano, there's a reverse polarity prevention diode that drops 0.3 to 0.4 volts between USB and the 5V bus.
Surprise when you power it with an external power supply the A/D readings will be different. Your 5V will then go to 5V or close.
Thanks for help!
yes it is kind of annoying. Since that ADC performance is not critical to my project, I can only do the calibration once before the program goes into loop().
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