Suppose two functions have the same domain and different ranges. Plotting them together using
Plot uses the same scale for the

values. To compare the functions,

plots them with different scales for the

values (on the left and right) so that their ranges appear to be the same.
Here it is not obvious whether there is a simple relation between the two functions:
The custom function defined here,

, rescales two plots to appear to have the same

range. The ranges of the functions are shown on the left and right sides of the frame:
The combined plot illustrates the fact that

for some

and

: