I believe AA like BSA and many other rifle makers use the 23mm mini high pressure gauges from the mini gauge co, other than rotating the face to zero them there is no other way to adjust them.
they are a pretty standard item with an 1/8bsp thread so not too difficult to find a replacement.
The one on your dive bottle can be adjusted, there are several links in the back of the gauge so the zero position of the needle can be set and also the rate of its rise in relation to pressure can be adjusted, unless you have a known accurate gauge to set it against having the ability to be calibrated is not much use. Yours may have taken a knock which has bent one of the links.
HFT, for people with only 2 buttucks!
VooDoo TwoTwo The next chapter.