TOOL LENGTH GEOMETRY

Hi
Can anyone here help me with my problem?
I have a Haas VF2 2007 model, my problem is, after my first set of tool length geometry and tried to re-set the length again, it gives a different value from the first. I'm using a z axis zero presetter and it gives me a difference of .004".
I already change the thrust bearing of the z axis but still same problem. I also change the parameter 127, still same result, i can't get a stable depth result on my workpiece.

Thanks in advance.