It's OK, I've been on a course on how to use plumb lines, at least I hung around there for a while.Sorry JBR but unless you have had the PL3 training and the consequent health & safety certificate, you are not qualified to use it. I think I might have to report you to Brussels.I have a plumb line that I made myself from a nut and a piece of string. That works perfectly, and it was free!