The Extech PH100 ExStik Waterproof pH Meter with Flat Surface Electrode is an accurate, rugged and reusable stick pH meter with some unique data storage features that make it exceptionally easy to use and considerably enhance its usability. The flat surface electrode allows you to measure pH in liquids, semi-solids and solids and limits electrode breakage and clogged junctions. The Renew indicator tells you when it is time to replace the electrode. The CAL alert ensures consistently accurate readings by telling you when you need to recalibrate. A Memory feature records and recalls 15 sequentially tagged readings, so you will know how your readings have changed over time. The LCD readout displays pH, temperature and an analog bargraph that shows trends in acidity or alkalinity and indicates when the reading is stable. 1, 2 or 3 point calibration automatically recognizes buffer solutions. Other features include automatic temperature compensation, auto power off, low battery indicator and data hold.