Highest 2% RH accuracy with Grains Per Pound (GPP) Display. The Extech RH490 not only measures relative humidity in 30 seconds, the handheld instrument captures dew point, wet bulb, temperature and water vapor levels (Grams per Kilogram and Grains per Pound). This utility tool will store maximum and minimum readings until the memory is cleared and includes a data-hold button for rapidly fluctuating measurements.