I like the Pultec EQP-1A quite a bit and had a decent clue about how the controls interact, but this video from Creative Sauce explained it very clearly along with showing the resulting EQ curves as you manipulate the controls. He also includes some tips/tricks for usage. I'm sure there are other good videos out there too, but thought I'd share this one. I like this guy's style. He has lots of other similar vids as well. I'm finding them helpful as I wrap my head around some of the new plugins I got during the holiday sales.