A portable sensitive differential manometer is described. The instrument consists essentially of a train of gears from a small jeweled wrist watch movement and a drum covered with a rubber diaphragm. The design is such as to permit the measurement of rapid and slight variations of pressure. The pressure variations may be as small as 0.0012 cm of mercury and as rapid as 15 per second. The above sensitivity may be increased by a factor of approximately 10 by increasing the effective volume behind the moving diaphragm.