This was supposedly when beer cans were made of steel.

As the story goes, a sport cruiser was having problems with the compass but only at times and during the day was always different.

The problem was that when they first started out the compass was off as the cooler near the compass was full of beer cans, during the course of the day they drank the beer and put the empties somewhere else. At the end of the day, the compass was fine. Unless of course they put more beer in it and then it was off again.

It doesn't take much to cause a small fluctuation.