In a calculation the numbers used are often approximate, as
when they represent lengths measured to the nearest centimeter.
When this is the case, the result of the calculation may be
rounded off to an appropriate number of decimal places that
is the number of figures to the right of the decimal point
after the rounding process.
When rounding off, the last figure to be kept is increased
by 1 or left as it stands depending on which the number is
nearer to. For example, 32.8632 is nearer to 32.86 than 32.87
so to 2decimal places it is rounded to 32.86. But 32.8682
is nearer to 32.87 than 32.86 so it is rounded to 32.87 to
2 decimal places.
The size of the figure immediately to the right of the ones
to be kept is critical. If it is 5 or more then the remaining
right-hand figure is increased by 1. If it is 4 or less, then
all the remaining figures are unchanged.
The following examples illustrates what may happen:
4.9528 becomes 4.953 to 3 decimal place
4.95 to 2 decimal place
5.0 to 1 decimal place