The commands in Synchronization toolbar let you synchronize the orientation and position (i.e. zoom factor and center position) on both sides.

:
applies the same view command with the same view point on both sides, e.g.: Original state of the comparison window:

a zoom out is performed on the left side, it is performed on the right
side too.

:
applies the same view command with a different view point in both windows,
e.g.:The view points are different on both sides:

a zoom out is performed on the left side, it is performed on the right
side too, but the view points remain the same on both sides.

If the view points are different, pressing
on one side will bring
the other side at the same view point.
and
apply to the
following commands:
- View point modification with the pointer,
- in the View menu: Fit All In, Zoom In Out, Modify
(Look At, Zoom In, Zoom Out, Normal View), Named Views...