I think it is hard to come up with zoom function icon graphic symbols which are easily visually differentiated and remembered.
Perhaps they could be done as a magnifying glass outline with a different letter embedded within the lens area of each:
+ zoom In
- zoom Out
A zoom All (or Auto)
B zoom border (still thinking about this)
M zoom Move (pan)
P zoom Previous
W zoom window
? show current numeric zoom scale factor (needs dialog box)
N set numeric zoom scale factor (e.g. zn135.246) (needs dialog box)
The letter could possibly be chosen to match the hot-key short cut (e.g. ZA = Zoom All).
One disadvantage is that each supported language would need its own set of icons, but that is already needed for Asian languages anyway. Universal icons just means everyone has the same level of difficulty.
Are the "PageUp" or "Page Down" keystrokes already allocated? If not, could we assign them to Zoom+ and Zoom-?
Actually I was thinking about asking to remove some of the zoom icons :)
I'm not a professional CAD person and can't tell what those people do but I use the zoom icons at very very rare intervals.
Zoom icons I use (cant't remember teh last time I used them) are mostly "Auto Zoom" and "Window Zoom".
I mostly use the mouse wheel for zooming and panning.