When calculating with decimal numbers, plenty of attention must be paid in order to achieve accurate results. When calculating with a calculator, we can get numbers that could be replaced by any number. The values of all figures obtained cannot be relied upon. Significant figures indicate which of the digits in the number are accurate and which are not.

Example 2

a) The integer 500 000 has one significant figure. 
b) The decimal number 0.250 has three significant figures. 
c) The decimal number 0.04 has one significant figure. 
d) The decimal number 89.20 has four significant figures. 
e) Integer 4005 has four significant figures. 
f) Integer 540 has two or three significant figures, depending on whether the number is rounded. 

When a decimal number is truncated, the final significant number is incremented by one if it is followed by [[$ 5, 6, 7, 8 $]]​ or [[$ 9 $]]​. When rounding decimal numbers, the decimals after the truncation point are omitted. When rounding integers, the numbers that follow the truncation point are replaced by zeros.

Example 3

Round the numbers from the given point.

a) ​[[$ \text{4.57|392} \approx \text{4.57} $]]​

b)[[$ \text{0.609|75} \approx \text{0.610} $]]

c) [[$ \text{5 41|5 880} \approx 5 150 000 $]]

The sign [[$ \approx $]]​ is read “approximately equal to”.