The HI98129 Combo tester from Hanna Instruments is designed for fast, efficient and high accuracy pH, EC/TDS and temperature measurements. No more switching meters to measure the pH and then the EC or TDS of a solution. This tester has a hold feature to prompt the user when to take the reading & a display freeze for easy and accurate recording. Calibration and temperature compensation is automatic. The combo has a replaceable pH electrode cartridge and an EC/TDS graphite electrode, which resists contamination. The temperature probe is stainless steel, for faster and more precise measurement.