I just got home from a gig that had a problem which did bring this thread to my mind. Partly broken cable under concrete floor, with some moisture. It somehow generated its own voltage, so that i got negative resistance in one way, positive in another. Fluke 87V handled it exactly the same. So both meters gave somehow reasonable value in one way, but when crossing the leads i just knew that both values are useless.
Now that i got more involved in this, i wanted to try this in more controlled environment and realized that an empty AA-battery could do the trick. First one i grabbed had ~0,7 volts in it, nicely low and in range that i felt comfortable to poke with my meters at ohm-setting.
As I said, mooshimeter and fluke “warn” about problems in resistance measurement, if i happen to measure in “wrong” polarity, or try both ways. So 50% change to find out of problems at first try.
5 cheaper multimeters that i had at my hands reach all gave positive resistance readings, no matter what polarity i gave them. There were quite big differences in how they handled that situation though. Some went totally crazy and just flashed from range to range, some seemed quite smooth, but did not seem to stop wandering at all. Different polarity values were way off of each other, which is a good sign as its possible to realize screwed results with double checking. If measuring totally unknown things, you could believe your first result and just think that it needed some time to settle for a reading.
So, mooshimeter works like the big boys and thats a good thing. I’m positively surprised also about those cheap meters. Now that i know how they behave, I’ll probably remember to check at different polarity, if something seems odd and i cant get stable reading. I have done that in the past, but never had interest to examine what is really happening.
Now i know a little bit more how my tools behave.
My final verdict is: Measuring resistance is like measuring speed for land speed records. It’s only official when done in both directions in quite short time window.