Opti-pac is here on bench, tied into a $30 Clarostat optical encoder.

What it does here on the bench, Tied into X=encoder for a trackball..
it makes the cursor scroll across the screen. It has two serial ports,
a serial to USB cable and a jumper to configure for USB.

With the basic stamp, I could outrun the cpu speed with the small
diameter clarostat encoder (pulse width too narrow). DOES not appear
this one does. it has about a 40 pin chip on it.

If it reads the narrow ppr of the clarostat, the 600 ppr encoder
would be magic.

NOW, getting the cursor position with ansi Sys, making it register to
the software. < keeping it in a box on screen and adding it into the
DRO> will be pretty simple. NOW a keyswitch to enable or disable
software will be needed. ANY mouse-movement will register on the
screen DRO.. SO, main mouse will have to be disabled to make this
work. A couple of home Zero switches too.