The Extech PH50 Waterproof pH Pen has a pH range of 2 to 12pH with a LCD display that shows the pH readings. It makes it easy to calibrate a single CAL key with the automatic pH buffer recognition (4, 7, and 10pH). The user has a choice of a 3 point calibration for better accuracy. This pen features the data hold which freezes the readings on the display and a low battery indicator. Product also features auto power off to help conserve the battery life. The Extech PH50 Waterproof pH Pen comes complete with a built in electrode, a sensor cap, an inner pH electrode protection cap, and four LR44 button batteries.