jahlad - The blanking screw can be removed using an allen key.
Then if you put a low pressure one of these into that hole, it will give you the opperating pressure of the marker (ie what the vertical reg is set to)
Only worth doing if you have problems with this.
I had one on my cocker when i boughts it, but took it off, as once the pressure is set, that should be it. and i didnt want to risk getting the guage distroyed.
(it actually also dependes on what kind for front / semi block you have. only if the hole is bug enough and tapered to the right thread can this be done. but from wat your saying you knew that right?)