# Significant Figures

In the measured value of a physical quantity, the digits about the correctness of which we are surplus the last digit which is doubtful, are called the significant figures. Number of significant figures in a physical quantity depends upon the least count of the instrument used for its measurement.

## Common rules for counting significant figures:

Following are some of the common rules for counting significant figures in a given expression

**Rule 1.** All non zero digits are significant.

**Example:** x = 1234 has four significant figures. Again x = 189 has only three significant figures.

**Rule 2.** All zeros occurring between two non zero digits are significant.

**Example:** x = 1007 has four significant figures. Again x = 1.0084 has five significant figures.

**Rule 3.** In a number less than one, all zeros to the right of decimal point and to the left of a non zero digit are not significant.

**Example:** x = 0.000800 has only two significant digits. Again, has five significant figures. This is on account of rule 2.

**Rule 4.** All zeros on the right of the last non zero digit in the decimal part are significant.

Example: has three significant figures 8, 0, 0. The zeros before 8 are not significant again 1.00 has three significant figures.

**Rule 5.** All zeros on the right of the non zero digit are not significant.

**Example: ** x = 1000 has only one significant figure. Again x = 378000 has three significant figures.

**Rule 6.** All zeros on the right of the last non zero digit become significant, when they come from a measurement.