When performing calculations with measured quantities, the rule is that the accuracy of the final result is limited to the accuracy of the least accurate measurement. In other words, the final result cannot be more accurate than the least accurate number involved in the calculation. Sometimes, the final result of a calculation often contains figures that are not significant. When this occurs, the final result is rounded off.
The following rules are used to round off a number to the required number of significant figures:
a. If the digit following the last digit to be kept is less than five, the last digit is left unchanged. e.g. 46.32 rounded off to two significant figures is 46.
b. If the digit following the last digit to be kept is five or more, the last digit to be kept is increased by one. e.g. 52.87 rounded to three significant figures is 52.9.