VPI Alignment Jig

I have a question about the VPI alignment jig for the Scoutmaster, Seeing how it is adjustable how does one know with absolute certainty that it is correct. The people at VPI were suppose to set my cartridge up for me, when I put the jig on the TT to check their alignment I find that the stylis does not fall exactly where it should. It comes up a little short of the dot, this leaves me to feel that the jig is responsable. Any advice would be appreciated.