Oh, so if I give it a G29 n 3 T will it calculate the surface using 9 points and if I give it a G29 n 5 T will it calculate the surface using 25 points.

Also, how does Marlin determine what the surface looks like. Does it use all the points I tell it to use with G29 n ? T to define a single least squares plane or does it break up the surface into many different planes? I thought I read about some firmware out there doing this or trying to do this.