Thanks. The bubble issue seems to be common . I was hoping someone warranted against it . The notion of temp and elevation changes is nonsense . I have had compasses that developed bubbles with zero changes in either . Just setting in the drawer waiting to get back outside . Small bubbles are more cosmetic but large bubbles can interrupt the functioning of the compass and render it suitable for the retirement bend.  So what is an accepted limit on bubble size ? Who knows .  If you get lost then your bubble is too large .  A sad industry position on a troublesome issue.