My first discovery with the compass was that a road I had always figured was roughly north was in fact nearly directly west. That seemed implausible, since I knew I used the road mostly to get to a more northerly destination from where I was, and I was sure I'd remember if I had ever driven on it into the setting sun. But when I got down to thinking about it I realized I couldn't convince myself that I had ever been on that particular stretch of road anytime particularly near sunset. Usually I'd head out along it in mid-afternoon. So this was odd but possible. More peculiar, though, was turning from that road to one that I had always assumed was a bit north of eastward, and which I knew would get me to a more eastern location. But that road too turns out to be roughly south, according to the compass. This was hard to reconcile with my mental map of the vicinity, although it has to be pointed out that the roads around here are very twisty, and no two of them meet at a right angle, and even though a road may run primarily east-west that's no reason that the entire thing won't take odd turns to reflect the rich history of centuries of development based on where cattle used to wander.
Still, that got me to the real highway, a US Route with an odd number and therefore running primarily north-south. The northbound lane could run, plausibly, anywhere from northwest to northeast and not attract attention. So it drew my attention when it turned out the northbound side of the highway runs southwest.
After a bit more experimentation I determined that the compass has the potential to point in many directions, but mostly it likes to stick between south and west. I could shake it up and get it temporarily to things in the east or the north directions, but give it a good spin and leave it steady and it'll return to something south-west-ish. I wasn't sure how that was even physically possible. Apparently at some point the car has been struck by lightning and picked up a permanent magnetic moment, which would not surprise me at all at this point. But as I had the compass sitting on the dashboard for further observation, I also had to make a turn, and it leapt off the dashboard and disappeared somewhere within the car, not to be seen again. I presume that it's been eaten.
Trivia: In 1871 William Thomson (Lord Kelvin) was asked to write an article for the magazine Good Words about the marine compass. His first article on it appeared in 1874; the second part, five years later. Source: Compass: A Story of Exploration and Innovation, Alan Gurney.
Currently Reading: The Fabric of America: How Our Borders and Boundaries Shaped the Country and Forged Our National Identity, Andro Linklater.