Extech EC510 Exstik II Combo Conductivity pH and TDS Meter is designed to measure TDS, pH, temperature, conductivity, and salinity using one electrode. The EC510 Exstik II features an on-board memory that stores and recalls up to 25 labeled readings, adjustable conductivity to TDS ratio from 0.4 to 1.0, and an innovative "RENEW" feature which indicates when the electrode needs replacing.