I used two different methods using the stock Onefinity controller
First I performed testing to see the general repeatability of the sensor treating it as a probe wired to the controller where I created a g code program to run the axis toward the sensor at a feed rate of 50mm/min, when the sensor was activated it would stop and I had it record the offset from machine 0, then it would back off 10mm and run again with the following results (this is the Onefinity measuring itself in mm):
I then reconfigured the switch as a limit and changed the homing configuration to use the proximity sensor instead of stall homing. Homed it one time, move it 100mm away from the sensor and used that to zero the dial indicator. Ran the homing cycle again, back off 100mm and measure delta, repeated about 20 times with no variation in the measurements. Moved on to rebooting the controller then homing the machine followed by backing the axis off 100mm and again no delta in the measurements. Started thinking the digital indicator was playing tricks so I went to the mechanical dial indicator, same results. I moved the dial indicator base in a couple mm and re-zeroed the indicator just to make sure I wasn’t hitting a odd spot in the equipment but the results remained the same throughout.