This is a Three Star Challenge so you won't be expecting a quick
But as a hint : split the trace into chunks that mean
Firstly an obvious chunk would be the trace for one revolution of
the wheel because that's clearly going to repeat (the period).
You might notice that the first half and the second half of the
period match each other in a particular way - how would you
describe that kind of mathematical matching and, most importantly,
can you account for it?
All three traces have this property but the "same when
upside-down" quality isn't there for all of them.
What makes that "same when upside-down" work?