Wheelbuilding / Wheel Building / Wheel build help

the elastic band method is pretty good but your method above sounds slightly different and more complicated than the one i've used. I did this (from Sheldon):

1. Insert two old spokes into holes exactly opposite each other on the rim. Count holes to be sure.
   
2. Screw some nipples onto the spokes.
   
3. Pull them tight and measure dimension A in the figure (the diameter to the edge of the nipples, where the spokes disappears into them). Do this at several spots around the rim and average the measurements.
   
4. Measure the length of a nipple (dimension B in the figure) and add it twice (once for each nipple).
   
5. The result is Effective Rim Diameter (ERD). Thus,
   ERD = A + 2B.