I live in Denver, Colorado. Going above 10,000 ft. (3,000 metre) always results in an air bubble large enough for me to want to tilt the compass to prevent the bubble from interfering with the needle. Is that normal behavior for a compass?
I contacted the manufacturer (Brunton) which responded: "Extremely high elevations can cause temporary air bubbles to occur (also very cold temps can do that), so I wouldn’t be surprised if you see that with any liquid filled compass." Brunton kindly offered to replace my unit. I will measure the size of the bubble. If it does not exceed 1/4" there is no point in seeking a replacement.