Z value does not equal to zero when the tool touched the surface of workpiece

Hello. I use Paratec PV5 machining center with Mitsubishi Meldas 60 controller. After I set Z value of the surface, tool length, and offset tool and started the operation. The Z value shown in the position page does not equal to zero when the tip of the tool touched the surface of workpiece. What is wrong with G43 and how can I fix it? Thank you.

I'd love to know the answer to this also. I have just learned to live without my z display. I use the Distance to go to know if my program works.

AG