The result of a calculation involving approximate measured values must reflect the uncertainties of the original data; it cannot be more accurate than the measurements it is based on. Therefore the final answer should not have more significant figures than the least precise input. In multiplication or division, the result keeps as many significant figures as the number with the fewest significant figures. For example, 4.237 g divided by 2.51 cm³ gives 1.69 g cm⁻³, not 1.68804780876. In addition or subtraction, the rule is about decimal places: the result keeps as many decimal places as the number with the fewest decimal places, so 436.32 + 227.2 + 0.301 = 663.821 is reported as 663.8 g. Rounding off follows a convention. If the digit to be dropped is greater than 5, the preceding digit is raised by 1; if it is less than 5, the preceding digit is unchanged. If the dropped digit is exactly 5, the preceding digit is left unchanged when it is even and raised by 1 when it is odd, so 2.745 becomes 2.74 and 2.735 becomes 2.74. In a multi-step calculation, retain one extra digit in the intermediate steps and round off only at the end, otherwise rounding errors build up. Exact numbers and constants like 2π do not limit the significant figures.