That uses glass scales... Most DRO systems have moved to Magnetic scales... More compact, much more durable & easier to install...
I started with glass scales on my small lathe... Still using the glass scale on the Z axis but the X axis died, the glass scale being somewhat bulky was hard to mount & in spite of the shielding it got splashed with cutting oil which took out the infrared sensor... I replaced it with a mag scale, which being smaller allowed it to mount out of the way, it doesn't interfere with anything, it's safe from swarf & coolant & ever if it were to get coolant or swarf it's not effected...