The DP140 transducer includes 3/16 in. O.D. barbed brass pressure fittings, installed with 1/4 in. push-on tubing. For the shortest response times, use 3/16 in. I.D. for tubing lengths up to 100 feet long, 1/4 in. I.D. for tubing lengths up to 300 feet, and 3/8 in. I.D. for tubing lengths up to 900 feet. The static positive pressure port, labelled High, is located on the bottom of the unit. The reference pressure port, labelled Low, is located on the bottom of the unit. Use the reference pressure port for differential pressure measurements.