Altimeter, Simple, 28,000 FT., Zenith WWI and/or Post WWI

Here is either a WWI-era or Post WWI Simple Altimeter indicating height up to 28,000 ft. The knob rotates stiffly to turn the dial to adjust for ground height. The bezeled glass appears to be original.  

We have seen claims that these were used in aircraft such as the Sopwith Camel and Sopwith Pup, but these claims have not been independently confirmed by AeroAntique.

The pointer rotates counterclockwise as the aircraft climbs, indicating height of the aircraft along the outer scale.  As the aircraft exceeds 17,000 ft, height is read on the inner scale to 28,000 ft. 

It is in exceptional condition given its age, and we are proud to display it here as part of our private collection of historical artifacts. Measures 4.5 inch diameter and ~1.25 inches thick.