Scott - I think you’ve done a poor job in explaining exactly what you are doing. First step would be to put some paragraphs in your posts, it makes things a whole lot easier to read. It is also a common courtesy to not call your customers business practices stupid, trashing the competition.

Everything that I can ad up between your posts and the website tells me that you are using PSR Sky to plant, then using PSR Sonic, and PSR Tac to follow the rows that you made with WAAS. With that model you have eliminated GPS drift, and compensated for planter drift after the initial RTK pass by NOT using GPS. I am not aware of any non RTK GPS based system out there that totally eliminates drift, because of the properties of the orbiting satellites themselves.

Using the Sonic system to read and guide off the rows, tracks, marks etc, no doubt is a good idea for some applications, it looks to be well proven according to your website.  However it is not an apples to apples comparison with RTK or any GPS based system. Users of RTK know that you are steering the tractor, and the implement can go where it wants (assuming a drawn implement) depending on soil conditions which creates the variance. This is why the manufacturers have released or are developing active and passive forms of implement guidance to keep everything in line for subsequent passes (as you pointed out).

Hopefully this clears up some of the confusion for anyone else that reads this. Feel free to correct me if I've misinterpreted the technical information in your posts. Feel free to email me [email protected] .