So, let's say I have a precision voltage reference with the output fed to a voltage divider which is tapped at two places for voltages A and B. I've made sure to use precision resistors (or calibrate) and the divider doesn't overload the voltage reference. So at this point, I have maintained line regulation up to the taps but significantly degraded load regulation there by using a voltage divider for A and B but I thought that the best thing to do now is to use an op-amp voltage follower to buffer each of A and B. The characteristics that I've identified so far are that the input impedance should be very high, the input offset voltage should be as low as possible, low input offset voltage temperature drift and the input and output ranges should match. It seems like CMRR wouldn't matter in this application. On top of that, I'm not sure what else to look at. Noise should be low but how low and relative to what exactly?
To give a couple of examples, if I use the LM4040 4.096 Grade A then I should have, at worst, 14mV of error due to temperature drift and load, right? So how do I make sure that my buffer doesn't make that worse? What about something like the REF3240 where the error might only be in the tens of μV? Isn't it the case that something like the OPA340 would work fine in the first case but might not be quite good enough (just because of the input offset voltage and its temperature drift) for the second?