 A STEP-NC file is difficult to edit by hand because it contains geometry descriptions but for large programs the file size can be smaller because STEP-NC uses a compressed XML format instead of ASCII codes.STEP-NC is not the first attempt at providing better quality information to a CNC.The EIA 494 Basic Control Language (BCL) defined a control language that was portable and had toolpaths independent of machine geometry, but did not contain any of the other product model information found in STEP-NC.