A quick question about uncertainties and significant figures: Say, we have some numbers with a particular uncertainty 0.1 of each of them. What happens if the sum of these numbers has a greater amount of significant figures than each of the numbers alone? For instance, 1.01 + 9.99 = 11.0 or 11.00? (I believe it is the former) Then, suppose I keep the uncertainty of the sum 11.0, +/-(2 x 0.1), as percentage, say x per cent, and make some calculations. The sum 11.0 will then be changed. Would I have to take x per cent of the result? For instance, 11.0 x 2 = 22.0 +/- x%? Or should I not convert the uncertainty to percentage? If not, that if the units are different?