On Friday, May 9, 2014 4:44:38 AM UTC+12, James Metcalfe wrote:
At 23:50 07 May 2014, Bruce Hoult wrote:
(Better and worse, respectively, at the low-speed end.) Whereas your rule
is about 10% low throughout.

Yes, it's deliberately biased a little to the low side from the true (as you note) /4.7516 to make it more of a "guaranteed to pull up that far". Also useful for "I'd like to be down on that ridge line, but I don't want to overspeed". Of course in that case the height difference is going to be pure guess anyway.

I've contemplated using /4 for dives where you want to make sure you have some minimum speed, but I think that overdoes it. /4.5 would be better but not easy to calculate in your head.