Lathe tool height gauge - video

[Toolmaker51]

Andrew McGregor, please don't take this personally. I latched on to a word, not a person.

? Parallax? Why would anyone build a tool setting periscope, when a 6" scale twixt part diameter and tool tip is a 1 or 2 second endeavor?
Center height gauges; single greatest fetish of amateur lathe operators, and not less than 3 companies willingly cater with expensive gimmicks.
Ever see anyone using or even hinting at using such a thing in a substantially sized lathe; there is a reason!
There are lathes equipped with centerline gauges, typically those without screw tool height adjustments, just shims.
But none are optical; tactile and/ or contact only.