>>They explained that even high quality liquid units may develop bubbles. This is due to altitude changes and shouldn't affect accuracy.<<<br><br>Well, yes, they do say that, but you can sort of tell.<br><br>Obviously, if the case of the compass expands further/faster than the liquid inside for whatever reason (pressure, temperature), then you can get a vacuum bubble inside. These are usually pretty tiny, and tend to disappear if you warm the compass, or shake it. Many of the better units have a diaphragm of some sort, sometimes the whole bottom surface of the capsule is a diaphragm, that's designed to flex a bit and is intended to prevent the problem. Intended.<br><br>There’s another failure mode, though, and I’ve lost maybe 4 compasses to it over the decades. This is when there’s some tiny leakage at the seal/seam, and either air is getting in, or the liquid is sublimating or insensibly leaking out, or both. In this case, it starts out the same, but shaking and warming have little effect on the bubble, and over time it just gets larger and larger. This can effect the accuracy of the compass, especially those with a dial instead of a needle, as gas bubbles can get trapped underneath, and eventually, only part of the dial or needle is immersed- not good. Large marine compasses can be drained and refilled, but “recreational” compasses like the ones we’re talking about just hit the trash can. That’s what’s happened to two Suns, one Silva (a since-discontinued wrist model), and one Tekna that I’ve owned. <br>