Physics has always been my main interest; with more than a mere "favourite subject" label. Therefore I have made it one of my goals to not only be able to solve problems, but also express rigor and detail in my calculations. With regard to solving problems, I have 2 main questions: 1) Significant Figures I am familiar with the common practice in all of science regarding significant figures - the lowest number of significant figures in a question determines the number of significant figures in the answer. But what if a question has several parts, in which one should use one answer in the next "part". In that case, should one use the "exact" value from a calculator (√2, for instance)? Or should one stick to the significant figures rule and use the "rounded up" value? Which is the correct method? 2) Units I know and appreciate the importance of units in physics, and I understand that they should be explicitly stated in a final answer. But what about the working? I mean, while computing a derivative or an integral, should one include units for the coefficients? Do physicists actually show units while "doing the math"? Or do they consider this practice redundant and of no good use?