PH Tester 0.1 pH Resolution. Now offers automatic  calibration to one or two points, automatic buffer  recognition, calibrated buffer tags, stability indicator, low battery indicator, and selectable automatic shut off. The Checker plus still maintains the iconic pentagon design with a probe that measures 103 mm in length and tapered to a 8 mm diameter making it ideal for test tubes and vials. Economical - The Checker Plus is a full-featured pH tester at a price that anyone that needs to measure pH can afford.          Large LCD - Enhanced LCD that displays reading, stability     indicator, low battery indicator and calibration tags.