Switchable Gain Op Amp
write an error budget.

This requires 

1) understanding the detailed behavior of the entire circuit, 

2) determining the partial_derivatives at the operating point(s) so dVout/dR2 is
a known number.

3) algebraically summing the various partials, and see if the result (including ADC DNL &amp; INL &amp; quantization noise) is less than your 2% goal, at least 90% of the time.

4) or you can run a myriad Monte Carlo simulations, and pretend to be understanding your system