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| Significant Figures |
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| It is the expression of accuracy of a physical quantity. The value in digits, accurately known in a measurement plus one digit that is not certain, is called significant figures. Significant figures is directly proportional to the accuracy of measurement. Eg., a reading of 6.34 is accurate to 3 significant figures, while a figure of 6.342 is accurate to 4 significant figures. Thus, significant figures are all digits about which we are determining significant figures. |
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 Non-zero digits are all significant. |
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| Eg., 256, 34 has 5 significant figures. |
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 Between two non-zero digits, all zeros occurring are significant. |
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| Eg., 567.003 has 6 significant figures. |
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 Zeros to the right of decimal point and to the left of a non-zero digit, are not significant. Eg., 0.002564 has 4 significant digits. |
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 Zeros to the right of decimal point and to the left of a non-zero digit are significant. . |
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| Eg., In 1995.00 there are 6 significant figures |
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| In 0.019940, there are 5 significant figures. |
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 Zeros to the right of the last non-zero digit are not significant. |
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| Eg., In 199500, the significant figure is 4. |
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| The omission of the last digit, which is not required for correctness of a physical quantity, with least deviation from its original value, is called rounding off. |
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| One or two rules has to be followed in rounding off, like |
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 The rounded off digits should be removed altogether, at once. |
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 If the digit dropped is less than 5, then the preceding digit remains unchanged. |
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| Eg., |
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| a) When 6.83 m is rounded off to first decimal point then 3 is dropped. As 3<5 and 8 is retained, i.e., 6.83 m when rounded off, becomes 6.8 m. |
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| b) When 0.009037 m is rounded off to 2 significant figures, we get 0.0090 m. |
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 If the digit to be dropped is more than 5, then the next digit retained, is increased by one. |
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| Eg., 5.76kg when rounded off to first decimal place, becomes 5.8 kg. |
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 If the digit to be dropped is exactly 5 and is followed only by zeros, the preceding digit is increased by one if it is odd and retained as such if it is even. |
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| Eg., When 8.745 kg is rounded off to 3 significant figures, we get 8.74 g. |
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