congrats on 1st silver...more to come now.To answer your question about the f2 going haywire...like many machines the f2 is suseptable to emf interferance.a nearby cell tower just freaks out the f2.also ham radio antenna,underground or overhead electric service.even your cell phone can cause some problems at times.
The f2 is really an amazing entry level machine,my wife swung one for two years before switching to at pro.It does have its limitations tho.being a preset ground balance machine it can suffer greatly in high iron soil etc.
hope it helps...hh