The Hanna Instruments HI98107 pHep® pH tester is a rugged and reliable pocket-sized tester for use in the lab or field. This modern looking meter is only 0.7" thick and extremely ergonomic, fitting comfortably in your hand. The pH electrode uses a unique reference cell design that utilizes an extractable cloth junction. A clogged junction will typically exhibit erratic readings that will not stabilize. Simply extracting a small portion of cloth from the meter will clear any clog by exposing a fresh, clean surface. The ability to clear any clogging will extend the life of the pH electrode.