It seems like this offset was a known issue; Arduino actually provides code to calibrate the ADC on SAMD boards, which will “fix” the problem with software gain and offset factors, although ...

The Sno (pronounced like “snow”) board is a tiny footprint Arduino board that you can see ... In particular, there are modules to do analog to digital conversion, servo control, operate ...

Among all the Arduino boards, the Uno is most folks' go-to choice ... they can also be used to generate simulated analog values through a technique called Pulse Width Modulation (PWM).