The Sure Test® Commercial Lab Meter offers the ultimate in precision and accuracy. Dependably measure pH and conductivity (EC or TDS or Salt) and temperature (F° or C°) with ease. It also has the ability to measure Oxidation Reduction Potential (ORP) with the optional ORP probe (716398 - sold separately) - very useful when incorporating sanitizers (ozone, quaternary salts, hypochlorous acid, etc.) into your grow regimen. The meter uses automatic temperature compensation (ATC) for more precise readings of all parameters. Comes with replaceable conductivity probe (716394), replaceable pH probe (716392 - resolution of 0.01 and an impressive pH accuracy of +/- 0.02), and a 100v power supply and probe holder.