The method of using a layout assembly in Pro/E which has already
mentioned by others, where the components that you want to compare are
superimposed using placement constraints that make sense and contrasting
colors are applied to each (e.g. one is red and one is green), can be
enhanced by setting the view display mode to wire-frame. Although not
necessary, a personal preference is to set the background color to solid
white or black. Orthographic view orientations such as front, left, top,
etc. can then be used to key in on where differences exist (panning
around and/or zooming in if necessary). Reference dimensions can be
created, either within the context of the layout assembly itself or a
layout drawing that it is plopped on, to determine what the numeric
deltas are.
ProductView also has functions for comparing 3D models and 2D drawings.
Regards,
Dustin Neifer
General Dynamics Land Systems