@ DavidFC

It has always been my understanding that this formula was created by Harlan Grove several years ago.

This was like seeing an old friend again. So thanks for posting. Like you I (self taught) recall spending many happy hours taking this apart and putting it back together in various ways so I could learn array formulas. I nearly wore out the F9 key and Evaluate Formula (Fx) doing so. LOL

So keep "plugging away". The time spent in understanding this one is well worth the effort.