The Bluelab pH Pen is a compact, robust, and user-friendly handheld pen for taking accurate measurements of pH with increments of 0.1 pH. It is fully temperature compensated to ensure reliable readings, and fully waterproof so that it can float in reservoirs. It has a temperature display option in °C or °F and a hold function to keep the pH reading on the screen. Easy to calibrate, and with a calibration check mark to remind when recalibration is due, it is powered by 1 x AAA alkaline battery (included) with 350 hours of battery life, and has an auto shut-down after 4 minutes of unused time to save power.