The Extech HD755 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 13.85 in. H2O (inches of water). Max/Min recording and relative time stamp are useful features, as are HD755's Data Hold and Auto Power Off functions. The 0.5 psi HD755 also features Zero function for offset correction or measurement and a built-in USB interface.