Probabilities are normalized (scaled) so that the total area of the histogram is one square unit. Thus the area (not the height) of each bar is the probability of mortality in a two-year period. The data on which the histogram is based was obtained from the 1980 Standard Ordinary Mortality Table, Male Lives (Source: Black/Skipper, Life Insurance, Eleventh Edition (Englewood Cliffs, NJ: Prentice-Hall, Inc., 1987), p. 314.