The Dwyer LDPM01 Digital Differential Pressure Manometer, 55.4 in. w.c., 11 Selectable Pressure Units, 3% Accuracy is a versatile, handheld, battery operated manometer that can measure up to 55.4 in w.c. (140.6 cm w.c.). It is able to measure either positive, negative, or differential pressure with a 3% FS accuracy. Users can select from 11 common English and metric pressure units.