I thought it is more complex than that..otherwise they can derive the equation for multi-layer ferrite core inductance but there is none. The effective diameter increases if the wiring is inclined to the ferrite core axis. I looked through several valve radio design books and there is nothing about it. I read somewhere in Terman saying that the wave windings add about 10% inductance.
I have found a whole book devoted to coil winding techniques (machine only). It is more of historical interest:
http://www.vintagewindings.com/gen%2...%20Winding.pdf
I have tried crude, simplified winding (mimicking wave winding partly) by hand on a 6mm miniature plastic spool with SWG40. It is just about doable but the hardest part is to stop the windings sliding or losing the pattern. Of course it would not be as neat and complex as machine winding pattern.