[Mindless2112]

You either find out the candidate knows how GPS works or you find out the candidate's willingness to say "I don't know".

It's valuable to know how someone will handle a question they don't know the answer to -- whether they recognize their own ignorance and whether they are willing to admit to it.

[daenz]

There are plenty of ways to get to the bottom of what a candidate knows without resorting to unreasonable questions. What you're really testing for is a candidate's patience for being toyed with.

[lazide]

Or the candidates ability/willingness to bullshit in order to not look ignorant or unskilled in something.

Which is actually useful to know, even if this method would be a dickish way to do it.