tallaustin2276 asked: I recently finished building the rostock 3d printer and I have began to calibrate it. I have ran into a problem because when it moves parallel to the build platform in both the x and y axis, it dips up and down in a bowl shape. I don't know how to fix the problem. The nozzle is at the perfect height in the center and is too high in all the corners. Please Help!

This problem is very common and there are 2 ways to fix it:

Adjust your DELTA_SMOOTH_ROD_OFFSET up or down by one millimeter and see if that makes it better or worse. Then adjust by half millimeter, and so on, until your first layer is completely flat. Add the autolevel Z probe to your end effector. It will automatically calibrate before each print if you add G29 to your slicer prefix. This will detect the bowl shape and automatically correct it so that your print is completely parallel to the print surface, and the first layer thickness is always exactly right.

http://reprap.org/wiki/Kossel#Automatic_bed_leveling_probe