Easy user-replaceble sensor allows for quick sensor replacements, if needed. No tools necessary. Measure pH and ORP (oxidation reduction potential), or redox, quickly and easily with the 1003 combination sensor. The 605103 pH/ORP Sensor can be used with the YSI Professional Plus Multiparameter Handheld Instrument. Requires Cable/Probe Assembly. Not compatible with the Pro Series Quatro Cable.