If the tester was used or lay aside long time, recalibrate it. If you open battery case or replace battery: recalibrate it. Remember to gently wipe it with a clean, soft cloth when you are done before capping it again. Automatic Calibration. Our PH meter has a 2-point auto-calibration function that automatically recognizes standard liquids and completes calibration in seconds. Digital PH meter pocket pen-type water tester for aquarium water pool calibration. Just remove the protective cap and immerse the PH meter electrode in the solution and press the button to be measured. the sensors are very sensitive and the test data is fast and accurate. Delivery Quantity: 1pc Package Contents: Only the above package contents, excluding other products. Batteries are not provided. Size: 15.5*3.1*1.8cm (Reminder: The size is measured manually, please allow 1-2 cm measurement error) Color: yellow (Due to different monitors and lighting effects, the actual color of the item may be slightly different from the color shown on the picture.)