Never again watch your tester sink to the bottom of a tank or pond-—the OAKTON Double Junction pHTestr 10, 20 and 30 floats! Unique double junction electrode design and increased reference gel volume give you significantly longer electrode life, especially in harsh applications. Automatic Temperature Compensation (ATC) and three point, US or NIST buffers (4.0, 6.86/7.0, 9.18/10.0), push-button calibration provide high accuracy even under varying temperature conditions. Replaceable double junction electrode allows the Testr body to be used many times over. Operates on Four 1.5 V batteries with an estimated 500 hours of battery life. Certifiable to IP67 standards.