surface representations will not trap water. An example of the latter is given in the original
tolerance relation, R∼
1, of Example 3.11.
Another way to show this same information is to construct a two-dimensional contour
of the relation using various contour levels; these correspond to different degrees of
membership. The graphic in Figure 3.12 shows contour plots for the tolerance relation,
R∼
21
, and the equivalence level, R∼
31
. The contours in Figure 3.12a would trap water (the
lightest areas are inside other darker areas), whereas water would not be trapped in the
contour diagram of Figure 3.12b.