Once a line has been closed you may use that descriptor over again. If the program finds a MOD code, it will read the elevation modifier, change the elevation, and remove the MOD code from the descriptor. Line and curve codes. Line and curve codes tell the program how to connect the descriptor points. There are a variety of line and curve codes, including two shortcuts to close chains of points back to the starting point.
B begins a new line.
E ends that line. BE closes that line back to the beginning point. A BE with a PC or POC will close the arc back to the starting point. C on the third point closes a parallelogram back to the beginning point using lines parallel with the first two lines. POC is a point on the arc of a continuous curve.