I am using Arduino nano with the Atmega 328p.
VRef is internal (1.1V)
When the board is powered via the usb the supply voltage is 4.5V from my pc.
When I use an external 12v power supply ,connected to Vin ,(build in 5V regulator)the voltage is 4,96.
Changing between the pc and the external power source the reading differs with +- 0.3V.
I used a 12V batt to eliminate possible power supply noise,but the result still varies.
If the internal reference is fixed on 1.1V,why does the result varies when using internal or external power source.