A bell-shaped probability density on top, and its running total — the same distribution's CDF, climbing from zero to one — below, sharing one x axis from minus three and a half to three and a half. Two buttons switch the reading direction. In "area equals rise" mode, two draggable handles named a and b mark an interval: the area shaded under the density between them always equals the amount the running total climbs between the same two points, and readouts show both numbers agreeing. In "slope equals height" mode, one draggable point x carries a tangent line on the running total and a height marker on the density: the tangent's slope always equals the density's height, about 0.40 at the center and near zero in the tails. Dragging anywhere on the chart moves the nearest handle.

Read it in two directions

A bell-shaped density, and its running total collected left to right. Same object, two readings.