I've had 2 Dacor compasses that developed large bubbles. The first came with my original console. The second was the replacement that the manufacturer sent. I gave up and bought a Sherwood eventually. For the record, none of them have ever been on a plane, pressurized or unpressurized. They are always used in a well protected console, so I doubt that they were banged around too hard, although that is always a possibility. Almost all the compasses I have seen appear to be nearly identical , except for the Logo, although I can't claim to have seen every brand out there. I suspect that most all of them are made by one company, with "branding" to order from the customer.