I'm thinking this may be the cause of your erratic readings. The meter may not be properly designed to count 3-phase AC; only single-phase.
As for those worrying about using it on mains... I could see if you were talking 440 or even 240VAC; but 120VAC? Hell... one of the old codgers (admittedly, a bit off in general, but still) I used to work with at the Ding & Dent Appliance store would use two fingers of one hand to test for presence of live AC when puttering around inside of microwaves and the like. 120VAC really still qualifies as "low-voltage" IMO; hell I've seen 12VDC powered amplifiers with +80V and -80V rails.
Cheers, mnem
"Electrons may be very, very tiny; but when they gang up on you they always win." ~ me
I'm only reading a single phase at a time, voltage readings are accurate on each phase to neutral. It's the two "hertz" settings that act oddly, it could be the contacts in the meters "switch". I'll try to document the behavior in more detail this week, for those that like a good mystery.
And yes, I've heard the stories of the "old timers" using their fingers to detect voltage, never felt compelled to do it myself. Almost all of electrical readings I do are outside or in a studio, open air settings, temporary installations typical of most film and TV sets and locations. The few times I have to read a mains box in an electric closet or room, I would only probe with a "SAFE" meter. Most of the voltage we are exposed to is 120v. AC, and 220v AC measured between the generator phases. There are times when more power is needed in an underpowered studio, and the they rent one or two MegaWatt CAT generators that put out 480v AC, step down transformers are then used.