Interpolate

Selecting Interpolate causes the plot to rock between a plot of Y vs X1
and Y vs X2 if "Y Axis" is selected, or between a plot of X vs Y1 and X
vs Y2 if "X Axis" is selected.

The states set by the Rock and Interpolate buttons are mutually
exclusive, that is, selecting one causes the other to be 'deselected.'

Note:  Interpolate doesn't work when rotation is about an oblique axis.