To obtain the best service from any type of magnetic compass, it is advisable not to store compasses together in steel cabinets or drawers. Over time some of them may have reversed their poles. Liquid-filled compasses, including most commonly used brands, may develop a bubble in the liquid after a time. The bubble will increase in size with an increase in altitude and changes in temperature, but it does not affect the use of the compass unless it becomes quite large. The needle case can generally be replaced by the manufacturer or their agents.