The number of digits that are meaningful: they have an accuracy matching our measurements, or are simply all we need.

Example: we measure the garden to within 1 meter.

Our calculations give an area of 58.37215 m^{2}

But that is *way more* digits than our accuracy of measurement, so we decide to use 2 significant digits.

Our final result is **58 m ^{2}** (the two significant digits are 5 and 8).

More Examples:

• when we show a result like 4.500 we are saying we know it isn't 4.499 or 4.501

• but a number like 300 suggests we know it isn't 200 or 400

We can add a "plus/minus" (±) value to show our level of accuracy:

Example: 300 ± 10 says we know it is between 290 and 310

Have a play: