The END signifies the end of that command. It's probably a bit redundant since the command receiving bit automatically stops when a CR/LF is received, but it's kind of a way to validate the command. The pause itself has nothing to do with the END, and everything to do with the need to send a signal back to the controller to tell it that it is ok to send the next command. After each command is processed, the machine sends a "READY" back to the controller, and the controller will only dispatch the next command when it gets a message to say the machine is ready to receive one.

I'm positive that there's a smarter, maybe asynchronous way to do that that might let me buffer a command while it's busy drawing, but I haven't got it yet. Until that happens, there's a pause. PErsonally, I hated the blots that came from bleeding sharpies, because it represented a loss of control. But now, I love them, they're the hand of the creator (ie the cadence, the rhythm of the machine) in the drawing - they kind of show the working-out, and I've found people respond really well to them. Just buy pens that don't bleed (spirit-based ones are the bleediest, pigmented water-based ones are least bleedy) and your problem is solved 🙂 Trite, I know, sorry 🙂