It is in very nice shape for its age.  The glass and case are intact and the dial markings are clear and precise. The knob rotates a small triangular pointer around the circumference of the dial, presumably to set a limit or target angle of flight. Measures ~2.5inches diameter and ~6inches long.  Would be a nice addition to your collection. And how else will you ever know the angle of your attack without one?

Please note that seller does not represent that this specific instrument was actually removed from any aircraft cited in the description, but that any documentation referenced here is evidence that it is the same type number and/or manufacturer's part number, used in these aircraft, or if such numbers are not available, the item closely resembles photos of the aircraft's instrument panel.  We do our best to link instruments to specific aircraft, but Buyer accepts responsibility to perform the research to verify the item's use in specific aircraft.