black, thanks for the kind words - here is my theory:
Each stock has its unique cyclical structure - but all stocks pretty much follow the nominal cyclical model (5w,10w, etc.) However, how does an index derive its cyclical structure? Prior to 1980s, one could not trade the indexes, so the only logical conclusion (at least up to that point) as that you get the cyclical structure of a particular the index by "summing" the cylical structure of all component stocks.
Therefore, when I went back and looked the market action for NDX over the last 10 years especially when looking at the NDX rallies out of the 4/4/01 and 10/10/02 lows, these two rallies came out of nowhere from "standard" Hurst standpoint:
-in April 2001, the (standard) phasing 80-w cycle was pointed down and the 40w cycle was at midpoint yet we got a huge rally out of the 4/4/01 low (as the 9/21/01 marked the next 40w/80w low). Even weirder was the rally out of the 10/10/02 low - here you have 4-year cycle hard dow, 80-w cycle hard down, and 40-w neutral, yet there is this huge rally out of the 10/10/02 low, and then NDX and Nasdaq stay way above the October low in Feb/Mar-03 where the (standard interpretation" Hurst 4-year (and all smaller) cycle bottom.
So, I came up with a theory (and it's just a theory) that there maybe two dominant cycles acting upon NDX, spaced out by one 20w cycle - so, Apr-01 was the Group 1 (G1) 80-w cycle low, and Sep-01 was the G2 80-w cycle low. Furthermore, then Oct-02 low was G1 80-w and 4-year cycle low (meaning that a lot of stocks made their lows at that time), and hence the strong rally out of that low, and then the G2 80-w and 4-year cycle low is Feb/Mar-03 (where the rest of stocks made their 4-year cycle lows). And it appears that these two dominant cycles (assuming that in fact they exist) are far more evident in NDX than SPX.
So, interestingly, my G1 80w cycle low is due to bottom in Sep/Oct (and the G2 80w cycle low is due early next year) - so, it will be interesting to see how this plays out, but it's just something to keep in mind.
cash
ps - and as you imply, it's still an "art", not science, and hence airedale and myself will sometimes see things differently, but will be in sync most of the time. and, yes, it's an awsome theory.