the best way to show him is with the kanstul backbore comparer...
this way you can show two models on top of themselves and see the differece.... another way would be to compare each of their backbores using this web page with the schilke numbering system - that may make more sense for most people....
here is the link:
http://www.kanstul.net/mpcJN/Compare...ompareIEbb.HTM
-marc