3.4 Bar graphs
The following graph (Figure 9) records how the outside diameter of a hypodermic needle is related to the needle gauge number.
This is an example of data that do not vary continuously, but instead change in discrete jumps, and discrete data are often best represented using a bar chart. (An alternative name for a bar chart is a histogram.) To express discrete data as a line chart would be misleading, since it would give the impression that gauge number and needle diameter are changing smoothly all of the time, which is not the case (there are no half- or quarter-gauge sizes, only whole numbers).
If you wanted a needle with a diameter of 2 mm, what would be the required needle gauge number?
Figure 9 shows that no such needle exists. A 2-mm-diameter needle falls between gauge 14 (2.1 mm) and gauge 15 (1.8 mm). However, because 2.1 mm is closer to 2 mm than 1.8 mm is, you'd probably choose the gauge 14 needle.