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# Guidelines for rounding

There are three simple guidelines for rounding.

• Two significant figures for casual measurements.

The journey takes $\Tblue{13}$ minutes. The cake uses $\Tblue{250}$g of flour.

• Three significant figures for accurate measurements. These might be scientific measurements, or measurements where accuracy is important, such as building work.

The moon orbits the Earth in $\Tgreen{27.5}$ days. Its axis is tilted at $\Tgreen{6.58}$ degrees from the vertical.

• More than three significant figures for very accurate scientific measurements.

The speed of light is $\Torange{299,\!792,\!458}$ metres per second.

The journey from London to Paris usually takes 2 hours and 20 minutes by train.