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