Bluelab pH Pen measures the pH and temperature of solutions in your gardening system. This pen contains a LCD backlight display that has selectable units for Celsius and Fahrenheit temperatures. It is fully waterproof with, automatic temperature compensation, auto-ff, low battery warning, hold reading function and loop handle for easy dipping and gripping. The double junction probe (not replaceable) helps you read a pH range of 0-14.0 at an accurate of +/- .01 pH. Comes with a 1 year Bluelab guarantee.