Rounding a number with the accuracy specified by the number of significant figures given in the rounded value. So e = 2.71828… = 2.718 to four significant figures and = 2.72 to three significant figures. e−3 = 0.049787… = 0.0498 correct to three significant figures. Rounding to the same number of significant figures ensures all the measurements have about the same proportionate accuracy. If the units are changed, for example between centimetres and metres, then the accuracy of the measurements will not be changed if the same number of significant figures is used in the measurements.