What Are Significant Figures?

measure air pressure. When you record a measurement, you must always record the measurement up to the first uncertain number. A measurement always has a degree of uncertainty/estimation. For example in this illustration you can see that this pencil can either be recorded as being 4.72 cm or 4.73 cm. The last number in any measurement is understood to be the uncertain/estimated measurement. For this particular instrument, it would be incorrect to record the length as being 4.725 cm or 4.729 cm because the measurement would have two uncertain/estimated numbers. Again, you must record the measurement up to the first uncertain/estimated measurement.Significant figures are the numbers recorded in a measurement which includes all certain numbers plus the first uncertain number. Exact number, however, are different from significant figures. Exact numbers involve numbers that were not obtained by measuring devices but were determined by counting. Exact numbers are numbers related to counting not measurement. There is no degree of uncertainty with exact numbers. For example, in counting the number of fingers on your left hand, you count that you have 5 fingers. You did not measure that you have five fingers.

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