You should be looking for a change of state, rather than an absolute measurement. ORP is a relative measurement, and it is almost impossible to compare two ORP electrodes directly. ORP electrodes come equipped with bands made up of platinum, gold, or hydrogen, and each type will give you a different reading in the same solution. Even if the electrodes are of the same band type, the leak rate through the reference junction will affect your readings. Instead, simply measure two solutions and note the difference between the two electrodes. The difference between the two solutions should compare.
