Example of use of active-axes (see Axes.html ) and the Magnification (Zoom) tool [Zoom to Rect _ _ ]. The two displayed graphs are defined through the script [Step_function.txt]. Free movable on the x-axis is [x]. The tangent at the point s(x) = (x, f(x)) is drawn, and a 100-times zoom with focus at ó(x) is done. The rectangle D, which is magnified, is 100 time smaller than the red one and has its center at the point s(x). But it is so small, that the small disc, that denotes point s(x) covers it completely. The red rectangle is 100 times bigger than this small rectangle D. It displays everything contained into it, by magnifying it 100 times.