If you don't have time to read the whole thing and just want to learn how to add reasonably, I recommend http://en.wikipedia.org/wiki/Kahan_summation_algorithm

If you don't have time to read the whole thing and just want to learn how to add reasonably, I recommend http://en.wikipedia.org/wiki/Kahan_summation_algorithm http://en.wikipedia.org/wiki/Kahan_summation_algorithm