To the rookie question... "30 back" means that's how much line is let out before putting the rod in the holder or clipping it to the planer board line and letting it go out from the boat. Jets and dipsey divers run deeper the further you let out line so you can adjust the dept of your bait/lure by letting out different amount of line. There are charts to tell how deep the various divers/baits run at a given speed and line out. In general I would guess that a Jet 30 runs about 30 ft deep if you let out 100 ft, maybe 15 ft if you let out 50, etc. Dipseys differ a bit since they have a setting that allows them to run to the side. The more they run to the side the less the go down, so a 3 setting will be shallower running than a O setting, etc. You can do some trial and error by letting out enough that they hit bottom occasionally. Adjust half way to bring the bait/lure up half way in the water column, etc.

Hope that makes sense.