Where do you farm? WAAS is a free correction signal that available in the US and Canada.

I've never used any correction other than WAAS, but from listening to others I've concluded that all GPS corrections suffer from a certain amount of drift until you go to an RTK correction system. For broadacre farming, the question becomes whether the guidance drifts so much as to make steering un-reliable. In the last picture above, the time it takes to go down and back is nearly A half hour. It's hard to see much evidence of drift in the picture over that period of time. When farming North to South passes, I set the implement width 6" narrower when seeding and 16" narrower when working with the chisel plow. There are many days when that amount of tolerance is enough to work all day long with no need to shift to make up for drift. If I stop for the night, the line will usually need to be shifted the next morning to get me on track again. East - West passes are a bit fussier, but I think that's more a problem with orbit characteristics than corrections. We need more birds and we need them further north.

When spraying, I set the width to the actual width of the sprayer booms and try to spray when there is a bit of a side wind. Never any problems with skips, so far. Since I can't really see where I've sprayed, there's no way to shift anyways -- just need to trust the GPS and go.