[malaguti]

I recall someone here using something, Donchian channels perhaps to help with estimating, which was interesting.  Unfortunately I can't remember much of it.

I also note BadCharts use of the TrendAdviser diamond.  I tried calculating the stages of that system a while back.  It is logically defined, there is no ambiguity or human judgement, no wiggle room.

That may have been me, pcabc. I've played with donchian for some time
a close greater than donchian 40, along with a trend filter to enter or stage 2
a close less than donchian 20, along with trend to exit or stage 4
anything in between is stage 1 or 3
Reentry at various points in a stage 2 
I've been less concerned with stages 3 or 1 in all fairness as the optimum results is to hang onto your holdings, or reduce (not exit) at stage 3, exit completely at stage 4
the way I have it now is that a stage 4 might be a little late, but keeps me in a trend much much longer and not too late to eat into gains

the chart below is of the SPX without stages 1 and 3. blue is 2, 4 is red with reentry points at every pullback as long as stage 2 is in play