The Extech HD750 offers 11 selectable units of measurement. This differential Pressure Manometer can serve as a low range/high resolution gauge or provide differential pressure up to 0 to 138.3 in. H2O (inches of water). Max/Min recording and Relative time stamp are useful features, as are HD750's Data Hold and Auto Power Off functions. The 5 psi HD750 also features Zero function for offset correction or measurement and a built-in USB interface.