Is there any reason why I shouldn't store my compasses next to each other in my orienteering box?
If they are stored on edge, so that the needles can't rotate, you might end up with one that's pointing the opposite direction from the others, and the magnetic field of the majority can overwhelm the dissenter, with the risk that it will give in to peer pressure and reverse.
Supposedly there's anecdotal evidence in favor of that, people who have stored a dozen compasses together over the winter, and one or two point the wrong way when they're taken out. I have not witnessed that myself. I do have one compass that spontaneously reversed years ago, and I have no idea why.
A reversed compass sounds like the first building block for a great practical joke.
Protip: If you set your compass for the first leg from the start, and find yourself going back through the start call-up area, nothing on the map is making sense, and you've already checked that you didn't set the bezel north toward the map south, consider the possibility your needle has reversed. It took me about 45 seconds to figure it out. The second time past the start line is pretty embarrassing.
needle you see is usually just plastic and the actual magnet is attached under it. I have seen a case of magnet getting loose, shaking the compass made it to point to a new random direction but otherwise it behaved just normally.
I suspect manufacturers, wholesalers and retailers store and dispatch lots of compasses in close proximity.
School kits commonly store about 25 compasses right next to each other. Never had any issues.
Cedar, that isn't always reliable. I once ran on a course where the run to the start triangle was around 100m and then our course did a 180 and came straight back through the pre-start. I failed to see the point of it.
The one I have that reversed is not a plastic needle with a magnet, it's the old style with a metal needle. But it was all alone when it happened.
I've heard that the electromagnetic fields present around the small motors in cars - wipers, seats, doors etc - can cause reversal of a magnetic needle. But storing the compasses next to each other? No.
I have three compasses that are all stored together in a small bag, along with two e-punches and a couple of whistles. I have been keeping them in there for many years and never had any problems.
I'll note here that anecdotes about times when a rare event did not happen are... not data.
More concerned about changes in air pressure and bubbles.
Temperature and bubbles, too.
Falling on the compass and smashing it to bits...
Students with ‘therapeutic’ magnets stuck to themselves... (I wish I was making that one up)