AVR-Chat

> You'll most likely have to use a voltage divider to ensure that your
> analog input voltages remain below the maximum level.

You can also use an op-amp to subtract X volts from the input signal,
if you do that properly.  Op-Amps were originally intended as building
blocks for analog computers, afterall.   Another way, less precise, is
to put a zener in series with the voltage, useful for measuring the
automotive range, typically 9-14V. A 9.1V 1% zener shaves that down to
0-5V with small error, and preserves resolution across the range.