... use. 3.Water proof 4.High accuracy. Features:Data hold function for freezing the desired value. Supplied with pH 4.01 ... , pH 6.86, pH9.18 buffer.Microcomputer circuit, intelligent function, high accuracy. Compact size, light weightAuto Calibration for pH 4 ... (LR44) x 4 PCsMeter with pH electrode. PT-6020A PH meter ,Pen type digital pH meter