... for freezing the desired value. Supplied with pH 4.01, pH 6.86, pH9.18 buffer.Microcomputer circuit, ... accuracy. Compact size, light weightAuto Calibration for pH 4.01, pH 6.86 and pH9.18Power supply by 1 ... .5 V battery (LR44) x 4 PCsMeter with pH electrode. PT-6020A PH meter ... ,Pen type digital pH meter