The precision of a measurement is determined by the limits of the scale on the instrument being used. Precision is related to the smallest scale division on the measuring instrument that you are using. It may be the case that a set of precise measurements has very little spread about the mean value. For example, using a ruler with a millimetre scale on it to measure the thickness of a book will give greater precision than using a ruler that is only marked in centimetres. e.g. Paul and Phillis are investigating the boiling points of liquids. Paul uses an electronic thermometer that displays temperature to the nearest 0.1°C. Phillis settles on using an alcohol-in-glass thermometer, because she likes the colour, which can be read to the nearest 0.5°C. Unknown to Paul, someone has damaged his thermometer so that it is no longer properly calibrated. All his temperatures are too high by about 2°C. Phillis's thermometer is properly calibrated.
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