Center

This button toggles between two types of scaling methods.  Clicking on
the button creates an instantaneous flash and label change between Data
Center and Plot Center.  When the label is Data Center, the data will
be scaled from the center (midrange) of the data. This preserves the
shape of the scatter plot. When the label is Plot Center, the data will
be scaled from the center of the plotting window.  This facilitates
shape changes.  For example, when the data are all to one side of the
center of the window, the points farthest from the center will expand
out or contract in faster than points near the center.