[Voption]

referencing Metric vs. English units; You might be thinking of a space probe that was lost, due to just that exact problem. The Name of that probe escapes me, but in a critical part of the software, the Units weren’t consistent between metric/English. (I recall it crashed, but not sure if it was on the Moon or Mars.)
The Hubble situation involved the physical placement of a mechanical device they use to monitor if the grinding was proceeding equally across the surface. The test device wasn’t actually at the physical location they thought it was from which they calculated the various optical formulas. Somebody used a shim during installation of that device and that gap measurement wasn’t known to the people who used the device.

[TXnMA]

Thanks for sorting that out! The metric error was on a Mars mission. I'd forgotten about the shim and conflated the two spacecraft -- in my 80+ year-old memory... '-)

Maybe the Hubble correction was via the secondary mirror mount. Now, I'll have to go look it up...

[TXnMA]

Well, I did look it up -- and there's a fairly good article on the fix[es] -- at CBS, of all places:

https://www.cbsnews.com/news/an-ingenius-fix-for-hubbles-famously-flawed-vision/

...even if CBS can't spell, "ingenious"... '-)