Hi Therion mailing list, I'm trying to use the function "grade" in one of our .th files, theres a sketch made of a cave with very little detail, but we think it would be better to include it. I'm strugging to get the function grade to work, therion is giving me red writing "-- not enough data readings" and stopping the survey from generating, but only when I implement the grade function. I must be using it incorrectly, but I've tried it between survey and centreline commands too and that isn't working either. this gives red writing "-- invalid value -- centerline" centerline #[omitted] units length meters units compass clino degrees data normal from to length compass clino extend left grade UISv1_1 0 1 1.00 300 0.0 1 2 1.00 0.0 0.0 2 3 1.00 0.0 0.0 3 4 1.00 0.0 0.0 4 5 1.00 0.0 0.0 endgrade endcenterline Regards, Alastair Gott. AlastairGott@hotmail.com, M: 07931779380.