Significant figures

When measuring a physical quantity in the laboratory it is good practice to estimate the uncertainty on the value obtained. When such quantities are combined in a calculation it is straightforward, though possibly tedious, to combine these uncertainties to give the overall uncertainty. Frequently though, we are often asked to perform calculations using values where the uncertainty is not specified. In these cases we need to use some standard rules for combining the quantities based on the precision with which they are expressed,^1,2 to avoid giving values which imply a greater degree of precision than is justified. Before considering them, we need to understand what is meant by 'rounding'.