Used Hanna HI98108 pHep+ Waterproof Pocket pH Tester, 0.01 pH Resolution.

This meter tester provides high accuracy measurements in a rugged pocket-sized design. The simple two-button operation provides one button for ON/OFF, the other for calibration and an exposed temperature sensor that will provide rapid automatic temperature compensated measurements.

Note: Last calibration was done on December 11, 2025. Battery was also replaced on that day.