A long-delayed bench cleanup united these two HP 09872-60066 digitizing sights:
I’ve used the one on the right (above) with my HP 7475A plotters, but the other sight obviously won’t fit:
The metal-shell version is advertised as “09872-60066 Calibration Pen for fit HP DesignJet 2000CP 2500CP 2800CP 3000CP 3500CP 3800CP Original New” which makes absolutely no sense, as those were inkjet and laser printers with (AFAICT) no need for a “calibration pen”. Because nobody with those printers will buy (or even look for) a widget they can’t use, the price is surprisingly low, compared to the real ones occasionally found on eBay.
My guess: somebody halfway around the planet found a pile of Genuine HP plastic snap boxes, filled them with knockoff sights vaguely similar to the original (perhaps intended for a different plotter?), and marketed them with the usual (lack of) attention to veracity.
Anyhow, we find our contestants standing in the light on a micropositioner under the microscope:
The old sight (genuine HP plotter) has a clean field of view:
With a tidy dot in the middle:
The new (to me, anyhow) sight has rather coarse hexagonal light pipes with a gaps at the edges:
The spot at the middle is raggedly machined / drilled, with a bottom sufficiently un-flat to prevent focusing on the whole thing at once:
I have a vague project in mind to turn the new (craptastic) sight into an optical alignment punch, but the spot seems a bit too large for that.
The Smell of Molten Projects in the Morning 
Curiously, my HP sight looks exactly like your “craptastic” one, except it fits perfectly when manually inserted (you can’t carousel/changer load these things) and has a very crisp centre dot:
https://scruss.com/blog/2016/05/17/pen-plotters-not-just-output-devices/
Soooo there’s a difference between your HP7470A and my HP7475A: that big sight simply does not fit into the 75A’s pen holder (or the carousel, no surprise).
I definitely would have lost money on that bet!
I’m surprised at the difference too. Mine fits in a Roland DXY flatbed pen holder too, where it’s almost bearably useful. The 7470A is rather cramped to work with
Perhaps a quick visit to Mr. MinilaThe with a very sharp hss cutter would both ensmallen the dot and flatten the face…
Depends on whether it’s glass fiber or plastic fiber. In days gone by, I’d expect HP to use glass fiber, but, given the overall low quality, who knows?
I suppose I can try scratching the lower surface (in an inconspicuous spot hah) and proceed accordingly. If it’s plastic, using abrasives would likely be less exciting and give me an opportunity to use some plastic refinishing glop I got a while ago. Of course, this will require at least one alignment fixture …