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# Significant Figures

## 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.

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