Pair of Apollo Command Module (Block I) differential pressure gauges, measuring 2.25 x 2.25 x 1.5, manufactured by the Glassco Instrument Co., both bearing green labels identifying them as "P/N G-3877" and "NASA P/N 20M32076," with manufacture dates of November 1966. In overall fine condition. These pressure gauges were installed in the docking tunnel to provide the crew with awareness of pressure difference between the Apollo capsule interior and the exterior of the forward hatch.
