How to compare two frames side by side:

By selecting the "Two viewports" option, the left and
right halves of the screen are split and used as
separate windows into the data.

Each side can be scrolled independently and have
different highlighted lines.  Each side may have its
own marked frame.  Format options (time displays,
two-station display, etc.) are common to both windows.

Using F4 to zoom a single window to full screen size 
is particularly handy because the windows are small.
