The Milwaukee MA840 is a polarographic replacement probe with 3 m cable length for the Milwaukee MW600 Pro Dissolved Oxygen meter.The refillable polarographic probe has an oxygen-permeable polytetrafluroethylene (PTFE) membrane sensor for measuring dissolved oxygen (DO) levels in aqueous solutions.The probe uses a platinum cathode and a silver chloride anode which the MW600 meter polarizes so that oxygen passing through the membrane can be measured to produce stable, accurate readings.