CAISSON Stainless Steel Gauge 

The Caisson Gauge is used inside the chamber and reads ambient chamber pressure. Accuracy is maintained
for both increasing and decreasing pressures and always indicates true gauge pressure and/or a simulated
depth in a chamber.

Self-contained gauges with sealed Bourdon tube; require no pipe connection.
Designed to indicate the ambient pressure above any specified normal,
usually, the air surrounding the gauge above atmospheric, as in caisson work.