【BEFORE USE】: Put the included potassium chloride powder into 20ml of pure water and mix well. Then put the probe into the solution for 24 hours, take it out and clean the residual solution on the surface of the sensing bulb. You can now start calibrating. (Note: If the sponge is wet enough, skip this step.) 【WHILE IN USE】: If the calibration is inaccurate, repeat the "Before use" step. If you are using your own potassium chloride powder, make your own solution by adding 61.5g of KCL to 250ml of water. Then put the probe into the solution for 24 hours, take it out and clean the residual solution on the surface of the sensing bulb. You can now start calibrating. 【AFTER USE】: To ensure the sensitive bulb is active, add a drop of freshly prepared potassium chloride solution to the sponge inside the probe cover. Also, to better maintain the activity of the sensitive bulb, add the solution to the sponge every two months. ▶【Notification】Calibrate once a week if you often test PH 10 solution, or once in the middle of a month for neutral solutions. The 250ml calibration solution for multiple uses (about 10ml each time). Then rinse the electrode with pure water before the next test. Rinse and let stand 3-5 minutes before changing from strong acid to strong alkaline and vice versa. ▶【Auto Calibration】Let's make your job faster and easier than ever with this handy PH tester! With 3-point calibration procedures, your PH tester will automatically identify calibration solutions to give you your reading at any time. ▶【Automatic Temperature Compensation】 Temperature can affect reading levels, our PH meter's automatic temperature compensation can ensure you get the best reading possible. Unlike other pH meters that only have a 0-50 degree range, ours has an even better 0-70 degree range, so you can test with confidence in any environment. ▶【Clear Digital Display with Alerts】Tired of squinting at a small screen to get your readings? Take advantage of this pH meter's large, backlit LCD display that displays information in an intuitive layout so you can see even in low-visibility situations. When the PH value is lower than 3.5 or higher than 12.5, the white digital display will turn red and flash to warn you.