If you've never used one before, you should know that they will need to be
recalibrated occasionally with at least 1 or 2 calibration fluids (4.01 pH and/or 7.01pH typically).
Also, the probe will need to be stored in a storage solution when not in use.
The Millwaukee brand's user manual says that the 4.01 pH cal. solution can
be used as a storage solution.