I've used a number of different ERD measuring methods over the years. Wheelsmith's rods, Southerland's tape, Sheldon's spokes, DT's chart w/ nipples and the straight rod one I already posted. I fall back on DT's chart, lately often with a double check using the Southerland system. (I just had my original DT chart laminated and photo copied). As has been mentioned how one uses whatever system is most important. Getting use to the nuances of the tools one uses takes time and repetition. It is this step that most newbies avoid or don't have the chance to do. Andy.