This digital hand held instrument is used to measure differential pressure in the range of 0 - 5 psi. It also measures in various units like inh2o, psi, bar, mbar, kpa, inhg, mmhg, ozin2, fth2o, cmh2o, kgcm2. It also has data hold, auto power off and rs-232 pc interface facility all sales are final. No returns accepted. Replacements will be done only in case of the wrong item shipped or any manufacturing defect reported which (should be replicated at our end on receiving the product back).