Lexis diagram is the diagram for displaying the simultaneous effects of the two time scales (generally age and calendar time) on a rate. For instance, mortality rates from cancer of the cervix rely upon age, as the result of the age-reliance of the incidence, and upon calendar time as a effect of changes in treatment, population screening and mush more. The basic feature of such a diagram is a series of rectangular regions corresponding to the combination of the two time bands, one from every scale. Rates for these combinations of the bands can be estimated by allocating the failures to rectangles in which they happen and dividing the entire observation time for each subject between rectangles according to how long subjects spend in each. An instance of such a diagram is given in the figure drawn below.