http://archive.gao.gov/t2pbat6/145960.pdf
Page 2
dug into reference 48 from Wikipedia which referenced this article which I did a search on google.
It is however a good explanation why it remained undetected.
Arguing about whether or not something is a bug is pointless precisely because someone will just pull the "behaviour outside of expected use is undefined" thing out of the bag. Regardless of whether or not you should have expected something to work, if your product unintentionally kills people due to a software error, you have a gigantic problem. It's really that lesson we have to keep in mind.
I get this all the time from project managers: it doesn't matter if X fails because we aren't designing the software for X. But you can't just dismiss X -- you need to understand the consequences of X just in case somebody tries to do it. For example: It corrupts the DB if 2 people edit the same record at the same time. The project manager says, "Not a problem. I got sign off from the groups using the app and they promise never to have 2 people working on the same thing. Problem solved, and no need to modify the code!" Of course a week later the DB is corrupted and it's not a bug (it's a feature ;-) ).
It does make software development more costly, and you need to draw the line somewhere. This requires balancing risk. But I will argue that if you are writing software for a missile, there is no hiding behind the "we didn't design it for that" argument.
Its entirely possible to have any reasonable degree of precision reasonably required to the limits of our tools to measure.
This isn't about an inherent limit of computation its just programmer error.
"However, the timestamps of the two radar pulses being compared were converted to floating point differently: one correctly, the other introducing an error proportionate to the operation time so far"
The code had a defect that effects its aim from turning it on but because it took 100 hours to drift by 1/3 of a second the problem wasn't apparent when rebooted regularly. If software can't continue to do basic math without manual intervention its defective.
In fact everyone including the company that made it admits it's defective.
Its possible your teacher picked a great example to illustrate a communication failure.