@marvin7, i know this is off topic, but we already talking voltage dividers:
usually, when i build a voltage divider, i hook up my dmm and also the arduino and compare the values (voltage), continuously adjusting my bench supply from the min to max range.
what i observed, that the arduino vs dmm never outputs the same voltage on the full scale (from min to max) sometimes they are the same, sometimes there are differences around 0.05 volts, or even more. not linear. do you have idea why is this happening? (it happening the same on resistors or trimpots)
edit: i admit that my dmms are not in professional range, just something like this., this model is very cheap, but got very good reviews every where on the net.