Since I have my lathe with a U100L, I always set the Z zero with a master tool (z offset = 0), press CAL on the zero offset line, and that is it. Easy.
All all my other tools have their offset in relation to that tool/the face produced with that tool.

Now, I will probably sell this lathe, and the client told me that they work measuring the length of the material from the chuck up to the material end. Client does not want to change the way they work, so I am trying to reach a practical solution for this.

I have try to make some changes on the "zero menu" but none seams to work out correctly. In fact I was quite close setting a zero point that was indeed on the start of my chuck, then the measured entered in the "zero shift". This seamed to work out, but as soon I was in "MEM mode" to run the program, the value inputted on the zero shift went back to zero.

Thank you