The Sure Test? Pro pH Pen has a replaceable pH probe (#716396) and a larger display than other Sure Test? pH pens. Reads both pH and temperature (?F or ?C) with automatic temperature compensation (ATC) for more reliable pH measurements. Features a pH resolution of 0.01 and an impressive pH accuracy of +/- 0.05. 20 min auto power down. Single touch, adjustable calibration up to 3 points. Waterproof housing (IP65 rated). Pen comes with 4x LR44 batteries.