Bill Tindall
I was taught this tip and found that it works. One's eye is not sensitive to small differences in the diameter of the elements in a spindle, but their spacing must be precise. I make a story stick with a hook on one end to hook over the end of the spindle to be. The story stick has notches to locate the various elements-cove, bead, etc.). Hook stick over end of spindle and then mark off the beads coves etc. So long as they are spaced right it doesn't matter if say a bead on one part is slightly larger diameter than one on another part. This approach is so simple that duplicating devices are not necessary, or even an advantage.