Well, Holey can get to 1.5mm over the workspace with 12 measurements because it calibrates chain tolerances and includes chain stretch and sag.
SImply put, once Holey Triangular calibration will be mainstream, we’ll get on the next step: high accuracy MaslowCNC using correction grid values.
That is what I did actually: To acheive 0.5mm accuracy, I added a corection grid of measured position error values above the initial results of a well calibrated chain length computation model. And in that way, I would say @TomD 's “surper tape” application idea is partly implemented with a firmware version listed at the end of the post here, and using tape measures between a 3row x5 collumn grid of CNC marks, and a top beam contact surface for vertical position like item d here.
Improving the tape with the Caliper is a very interesting step!
To load a correction grid, I created a new B code that I send using a GroundControl Macro once after power up. See example here
Finally, when I used the Holey triangular calibration on it, the optimization tool basically reported I had optimal parameters. So I got the following comment on the Holey Triangular Calibration topic.