The machine that i have spent the last 5 years running was an Extron 4 axis machining center. I can't remember the model, infact i don't think we ever knew what model it was. But it was a relativly new machine, made in 2002. It was fitted with a Itri Mirl M2000 fanuc based Control.. I have tried googleing this control for any information but i couldn't find anything. Perhaps you may have access to better information.
At any rate i will try and explain how work offsets were handled in this control. It had a similar page to the HAAS Offsets page with all the offsets listed ie G54-G59. It also had another data entry page which had a drop down box to select which work offset to use (ie G54 etc) once you selected the work offset you wanted it updated the current readout position for that offset in the readout window within this page. It also showed the machine coordinates as well.
This page also contained 4 feilds X,Y,Z,A, in which you could load a preset value. If you loaded say -5.(mm) in the X field, when you pushed "Set X" button the current work offset (in this case G54) X position would be set to -5. This was ideal for use with the edge finder as it ment you didn't have to lift and move over 1/2 the dia. This was also usefull for setting any geometry of the part to any co-ordinate position you liked without phisicly haveing to jog there..
If you wanted to find the X center of the part, you set the X preset field to zero, touched one edge, pressed "SET X", move to the other edge, touch off and press the "1/2 X" button, the X axis offset value would then be halved, effectivly putting you zero in the center of the part.
It was so simple and required no hand calculation or joging back to the center.