Question

Which statement is correct one and how? 1- Which number has three significant figures? 2- Which number has three significant digits?

Answer 1

Either statement is correct, because they mean the same thing. For example, `"0.0505 g"` has three significant figures if three digits are needed to fully describe the uncertainty you have in your measurement.

The three significant digits, or significant figures, are "`"505"`". Read this question for more background on significant figures if you don't see why.

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In a greater context, consider measuring with a mass balance that has an uncertainty of `200` `mu g` (typical at my undergraduate university), or `"0.0002 g"`.

This means that if the above mass was measured on this balance, then you would report your measurement as `0.0505` `(pm 0.0002)` `"g"`, and your acceptable range for comparing to a literature value would be `0.0503 - 0.0507` `"g"`. A literature value outside this range would be considered statistically different.