Analysis of GIS Data by Simple Examination - Introducing Geographic Information Systems with ArcGIS - page 357

The terms accuracy and precision can also be applied to a set of readings or measurements. Again, a
classic example: Darts are thrown at targets. The target of person “R” looks like Figure 6-4.
FIGURE 6-4 Good accuracy and
good precision
Her dart throwing was both accurate and precise. The darts are where they are intended to be (accurate),
and very close together (precise).
Person S's target looks like Figure 6-5.
FIGURE 6-5 Poor accuracy but
good precision
The darts are tightly clustered (they hit a spot almost precisely) but lack accuracy, as they missed the
intended spot. (Perhaps some sort of systematic error is present—such as a breeze blowing up and to
the left.)
Person T's target is as shown in Figure 6-6.