The Bluelab pH Pen provides a compact, quick and handy way to manage the success of your crops to ensure maximum uptake of nutrients. Teamed with our Bluelab EC Pen or Bluelab ppm Pen, you have a handy, convenient and accurate system for ensuring optimum plant growth and health. Features: Measures pH and temperature, Selectable units for C & F, Backlit LCD display, Double junction probe (not replaceable), Successful calibration indicator, Hold function, Low battery warning, Fully waterproof, Auto off function, Automatic temperature compensation, 1 year warranty