Thanks for your time with the answer Jazz, most helpful! No, not sucking eggs even slightly, I'm in the happy position of knowing enough to know I don't know enough! :-)

I might have clarified what I meant better by substituting the 0,0 for a "corner of the work area" But, yes, I see what you mean. I'm interested in this thread as the design (Rev 872) I'm playing around with uses steel too, most helpful!