I found this antique on eBay for (somewhat) under HP’s 1980-era $35 price:
The prevailing price for HP 09872-60066 Digitizing Sights seems to be $100 and upwards, with outliers in both directions, so I just couldn’t pass it up.
Anyhow, the fiber optic pipe still works just like it did, back in the day:
The small dot in the middle is actually a paint-filled indentation on the bottom surface:
With the bottom flat on the target, the relayed image is in perfect focus:
The bezel recesses the top surface by 25 mil to protect the imaging plane.
OK, it’s a gadget gloat; I have absolutely no intention of ever chucking a piece of paper in the plotter and digitizing any points.