I am doing it the way I said and it is a manual operation, I need to chuck the "probe" and take a face and dia cut with the master tool and then I can set up any tool to that. If I have a part in the chuck and for some reason decide a tool, that I dont have set up in a slot, is needed my only choices are to estimate by touching off the part or take a light cut and measure or remove the part and replace with the probe.
What I was talking about was having a semi automated process with a probe that could be retracted and your probe was the reference so you would just put a tool in, make sure you are in a suitable position (manual part of operation) and then press a button, the probe would deploy, the tool would touch off in X and Z and the offsets would be set. No need for messing about machining the probe with the master tool first. That is why I said positioning accuracy would be the hard part and positioning in respect of not only X and Z but also in regards to trueness of X and Z axis of the probe.
Hood