Replacement probe for Hanna waterproof PHEP4 meter. When HANNA Instruments introduced its first version of the pHep (pH electronic paper) in 1986, it immediately revolutionized the standard in pH measurement. pHep's ease-of-use in combination with its affordability made it possible for non-technical and technical personnel alike to measure pH on the spot, accurately and inexpensively throughout a variety of industries. Since its introduction, over 1 million pHeps have gone to satisfied customers around the world. For this series, we have included all of the features customers have asked for and more! The pHep 4 includes features such as a dual-level LCD, battery level indicator, replaceable pH electrode cartridge, instability indicator, automatic shut-off and automatic calibration all in a floating, waterproof casing.