On a knee mill setting tool length is easy. Select your longest tool and call it 1 inch.
Put it in the quill and run the quill down one inch.
Crank the table up to touch the tool. Put each remaining tool in the quill, run it down to touch and record the length.
Now when setting up a job, take any tool that you will be using, put it in the quill, run it down what ever its length is,
crank the table up to touch. All of the rest of the tools are also set now. If you put a new tool in a holder you just
use one of the other tools to set the table position and then touch off the new tool and record its length.
You don't have to change anything except the new tool.
Setting up this way, Z zero is Machine zero and the tool length offsets the tool down. That means you can't have a Z+
move without a tool length in effect that is longer than the Z+ move.