does 250 require two electrodes? Or is it their requirement to be below a certain ohms that causes the need many times for two electrodes? I mean, shrink-swell soil, from what I have heard but have no actual knowledge, may cause you to need to go to a ring system of electrodes to effectively keep your ohms down, in all water levels in the soil. Unless I read that report wrong in the nineties in the Richmond Crimes Dispatch when they were going nuts over shrink swell soils in Va, and NC.