Apera Instruments, AI5562, PH8500-FT Portable pH Meter for Flat Surface TestFeatures:Equipped with Swiss LabSen 373 POM-body 3-in-1 Flat pH/Temperature Electrode designed for professional flat surface pH measurement.GLP standard data management, 500 data sets of storage, manual/auto storage, USB data outputQuick and easy 1 to 3 points of auto pH calibration, recognizing pH standards of 1.68, 4. 00, 7.00, 10.01, 12.45Intelligent Functions: Self-Diagnosis of out-of-range value and electrode invalidationAuto calibrationElectrode slope displayAuto power-offEasy parameter settingRugged Structure Design: IP57 waterproof rating; Soft silicone case gives you a firm and comfortable gripPowered by AA batteriesThe IP57 water-resistant structure makes the meter ideal for use in harsh environment. The rubber sleeve protects the instrument from general impact and gives you a firm grip.LabSen 373Powered by sensor technologies and key materials from Switzerland, Apera LabSen 373 POM-body pH Electrode is designed for flat surface pH measurement such as skin, paper, textiles, culture medium, etc. LabSen 373 pH electrode adopts a flat glass membrane with PTFE ring junction, making reliable surface pH test easier than ever.Specialized ElectrolyteApera's proprietary blue gel inner solution does not flow at all, which means it will never generate air bubbles. The electrode can work well even when being held upside-down. It is not only more convenient to use, but also improves the measurement accuracy by eliminating heat convection in the inner glass membrane.Long-Life Reference SystemComposed of a glass tube, AgCl, and a reference silver wire. The top end of the slim glass tube is stuffed with cotton, which prevents the reaction between AgCl and electrolyte when the temperature changes. It improves the stability of reference system and extends the service life of the electrode.