Precision of a Measurement and Significant Figures

Greetings,

This post covers one of the two general properties of a measurement; precision.  The other property, accuracy, will be discussed in a later post.  Together, accuracy and precision describe "how good" a measurement is.  Accuracy is how close a measurement is to a true or standard measurement.  Precision is how close replicate measurements are to each other.  Notice that accuracy and precision are very different, and so are discussed separately.

Precision and Significant Figures

The number of digits obtained by a numeric measurement and deemed to have an acceptable precision (all certain digits plus the first uncertain digit) are said to be "the number of significant figures in a measurement".
The following diagram summarizes this for a volume measurement using a 10 mL graduated cylinder with a scale of 1 graduation per 1 mL.

Note that by including the estimated digit as part of the measurement, the chemist "extracts" the most possible information from the measuring device.  Also the tolerance, which indicates the expected precision, is normally obtained by calibration of the measuring device.

My next post will discuss precision and rounding results of a calculation.

Have a good one!

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