I have a newer MM 252 at work. About 15 months old. Say i have the wire speed set at 240 every now and then it dips to 140 by itself. At first i though someone was messing with me but i mostly work alone and no one walks by it. Today it did it twice in the 10 hours i have it on. I put a chalk line at the pointer so i can watch it and the read out. But it didn't do it anymore. I had a new lincoln inverter at my last job that did the same thing and i too though someone was messing with it then some of the other guys were having problems too and we had 6 new lincolns. Just my wondering thoughts...Bob