This is an Antique / Vintage Short & Mason Surveyor Barometer – Altimeter Instrument…It measures 5 inches in diameter and 2 inches deep…It has a knob / dial at the bottom that turns the perimeter bezel to set altitude…Thick beveled glass has a tight crack running side to side…Quite Heavy…Has Short and Mason marking on internal mechanism…Though having the glass issue still a nice and somewhat rare example…Buyer Pays Shipping.