Caption: Accuracy and precision illustrated.

Features:

1. The horizontal axis repesents the value of a determination and the vertical axis the probability density for obtaining particular values.

2. The shown probability density curve is for a relatively precise, but distinctly inaccurate, set of measurements for reasons we discuss just below.

3. The terms accuracy and precision are used in various ways. Context decides the meanings as usual in communication. Sometimes the terms are used as synonyms.

4. In science, one common pair of meanings is:
   1. Accuracy describes the truth status of a measurement. High accuracy is close to truth. Low accuracy is far from truth.

   2. Precision describes the reproducibility of measurements.

      The width of the probability density curve for measurement outcomes is a standard measure of reproducibility. The narrower the width, the better the reproducibility

   3. Another common measure of reproducibility is the number of signficiant figures a measurement has.

      Every repeat measurement should agree to within signficiant figures if the number of signficiant figures has been assigned accurately.

      Thus, the measurement is reproducible to the the number of signficiant figures. The more signficiant figures, the more reproducible.

      Students frequently report insignficiant figures which gives those insignficiant figures the spurious appearance of significance.

5. The plot shows relatively high reproducibility because all the possible measurement values are confined to a relatively narrow range.

   However, that range doesn't include the reference value which we assume to the true value. Hence the measurements are rather precise, but are rather inaccurate---none of the them agree with the reference value.