I’m going to need a DeLorean for this one and go back in time. There are a number of tools available that I can recommend based on first hand, albeit somewhat dated, experience. They include the Membrane Tester, Polarizer, Dust Caps and Calibration Caps. You might also want to take a look at diatomaceous earth (toothpaste) for cleaning the anode/cathode. Here is a link to the BroadleyJames DO Accessories site for your reference. It appears to have everything I remember, but the toothpaste, and I believe these tools work with Mettler and Hamilton DO probes as well, but be sure to check.