In case anyone tries to fit the same device.....
It matters which way round you fit the sensors onto the sliders. There are three wrongs ways and one right way.
Not only must the black track be on the smooth surface of the sensor (with no screw holes), but the 1/3 of the black track with a "fat and thin" pattern must be on the cable edge, while the more even 2/3 of the black track must be away from the cable edge of the sensor.
If the DRO behaviour seems to be erratic, swap tracks ends.
All 3 axes now fitted and display mount made - seems to work well so far, now that I have reversed track ends on the Z axis.
Pity there was no manual to tell me all of this
good job this forum exists 
It matters which way round you fit the sensors onto the sliders. There are three wrongs ways and one right way.
Not only must the black track be on the smooth surface of the sensor (with no screw holes), but the 1/3 of the black track with a "fat and thin" pattern must be on the cable edge, while the more even 2/3 of the black track must be away from the cable edge of the sensor.
If the DRO behaviour seems to be erratic, swap tracks ends.
All 3 axes now fitted and display mount made - seems to work well so far, now that I have reversed track ends on the Z axis.
Pity there was no manual to tell me all of this
good job this forum exists
hexreader, proud to be a member of MetalworkingFun Forum since Sep 2014.