AVR-Chat

It depends on the accuracy YOU need. There are several
factors that contribute:

1. The referemce
2. The ADC conversion accuracy
3. The external circuit accuracy

If you use all 10 bits, then you can resolve 1 part in
1000, basically. 

But, if you use the internal reference, you are within a
few percent, at best. If you use Vcc, you are within the
accuracy spec of your supply (5% or worse, usually). You
can get external references that will do a lot better than
1% (but you have to pay for that precision).

If your reference isn't better than 1%, you won't get 1%
with 1% resistors. 

Jim
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