eBerry&reg; Portable Mini Digital Handheld PH Meter Tester Monitor Aquarium Pool SPA Laboratory Water Meter (PH Meter) the pH electrode into the pH value of 6.86 (25 oCc under standard mixed phosphate buffer solution, and gently shake. Measuring range :0.00-14 .00 PH. Accuracy: +/- 0.1PH. Resolution: 0.1PH- with a small screwdriver adjust the calibration potentiometer until the display value and the standard buffer solution at ambient temperature ph values. the electrodes into pH4.00 stupid phosphorus or potassium acid borax pH9.18 standard buffer solution. after about two minutes or so. Shows the pH value of the buffer value is compared to the error should be within the allowable range. This item can be used in: water purifiers and filters, food (vegetable, fruits) & drink quality monitoring, pools and spas, aquariums, hydroponics