Linear encoder / glass scale on manual knee LINUXCNC / EMC2

I'm at the point where my project (http://www.cnczone.com/forums/vertic..._retrofit.html) is functional and I'm looking to make it easier to use.

First on the list will probably be a pendant / control panel of some sort but I've been thinking about putting some kind of linear encoder on the knee so when I crank it up and down the controller knows where it is. Seem reasonable?

I'm sure someone has done this before but I searched and didn't find anything.

Hi i also did retrofit cnc machine.
I found an arduino based Pendant which i am now improved.
I am fighting now with cnc threading in the lathe. If you are interested search for handrad AT my page www.tkamsker.AT cu Thomas