Execution (computing) Puns

So, today was my CNC class. For those that don't know what CNC is, it's basically the computer programming, and execution of automated machining and manufacturing. To program it, there is a very long script you have to write to tell the machine what to do.

He was reviewing his own code in front of the whole class, when he realized something, he's missing an R-plane. He says "Where is my R-plane?" I respond, "Probably at the R-port"