A.S.M.E. Standard Internal Syphon Square Shaped Gauge by Jas. P. Marsh Corp.
Here is a cool vintage pressure gauge manufactured by Jas. P. Marsh Corporation. The gauge is labeled "A.S.M.E. Standard Internal Syphon." There is a large threaded fitting on the back of the gauge, which allows it stand up like a picture frame on a flat surface. The gauge has nice patina and rust throughout, and appears to be in good condition.