How to Calibrate the pH Meter:1. Rinse the electrode with clean water and wipe it dry. Turn on the pH meter and adjust to pH mode.2. lmmerse the electrode in the pH buffer solution and wait for the reading to stabilize. Press and hold the "CAL"button for 5 seconds the screen will display "CAL" and the pH calibration is complete when pH flashes 3times.3. Rinse the electrode with clean water and wipe dry.4.Repeat the above calibration steps to calibrate pHStorage:Buffer solutions should be stored in a dark, cool place (not in the refrigerator and at temperatures no higher than 25C) away from direct sunlight to prevent photochemical degradation. In addition, buffer calibration solutions should be protected from carbon dioxide from the air and stored in tightly closed containers.Colour:As ShownMaterial:plastictype:PH 4.0 7.0 10.0Package Contents:1 set x pH MeterOnly the above package content, other products are not included.Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.