I sent my Lyman in for service last week because it was behaving like it was taken over by Decepticons.
Without anything on the scale except for the pan it the screen would read 0 to 30 grains or so (up and down) on it's own. I tried everything customer support said: Don't use an extension cord, don't keep it near anything electronic (even a flourescent light bulb), wiped it down with fabric softener sheet, take of the silver base and brush out and granules, etc. Nothing worked so they finally said send it in. It was touchy to begin with. I built an adjustable mount for it that I could level the unit front-back and side to side. Breathing would make it move.
When it was working: I noticed the tendency to read over what you set it for after it (supposedly) stopped at the pre-set charge weight. I think it may be due to the trickler mechanism not stopping fast enough. So what I would do is set the charge weight some .10s lower than I wanted and used manual trickler to bring it up the last few tenths. I crossed checked the weights every so often with my beam.