""The deviation is about +1 to -1 units of ADC value maximum."

Yes Rob you are right. If I were Ramesh, I will be happy IF the above is REALLY the case. Once you reach these levels then EVERY darn thing can contribute to the drift - temperature, noise, individual chip characteristics. Also you would be better off to take the reading AFTER allowing a specified settling time. No component settles immediatley to its final spec. immediatley after power on - in fact some Instrument Amplifiers need 5 minutes (!) to stabilize. Not joking.

Please remember the overall accuracies or precision of any circuit is affected by all components in the chain and can degrade very fast cumalatively. Like if you have two gear trains with 0.9% efficiency each then when they are linked you get 0.9 x 0.9 = 0.81 and THAT is defenitley bad.


Raghu