Ok, not really a homework question, just something I am confused about. Hopefully it belongs here. Alright this is in my lab book: The overriding consideration for significant figures in computations is that a result should not be quoted with a precision higher than the absolute uncertainty associated with it. For example, it makes little sense to write I = (1.56250 +/- 0.01288) x 10^-2 kg.m^2, because the result is already uncertain in the third significant digit. It would be more appropriate to write I = (1.563 +/- 0.013) x 10^-2 kg.m^2 or, even better, I = (1.56 +/- 0.01) x 10^-2 kg.m^2. I guess I am just confused why its "already uncertain in the third significant digit". Can anyone explain.. like how is this known.