The digits that are known reliably plus the first uncertain digit are known as significant digits. Normally, larger the number of significant figures in measurement, greater is the precision of measurement.

Example : Consider density = 1.68804345545445 g/cm³

It is clearly absurd and irrelevant to record such a value of density. Hence, we follow certain rules for arithmetic operations.

• Addition and subtraction – 11.406 – 1.4 = 10.006 which can be rounded to 10.0 as the answer should have the same number of decimal places as in the number with least decimal place 1.4 (one decimal place)
• Multiplication and division – 3.8 * 0.125 = 0.475 can be rounded to 0.48 (As 3.8 has 2 significant digits, the answer should also have the same)