Calculate grade from lat/lon and elevation?

wayneh said:

I ride some rails-to-trails and most have grades of 1% or less. I've learned over many rides that it's hard to detect a grade below ~0.5% without instruments. For instance my favorite out-and-back ride gains just 100' in 10 miles. My outbound (uphill) speed will be about 2mph less than the return. Since my pulse is the same both ways, they "feel" about the same, I'm just going a bit faster coming back. Conversely a grade of 5-10% feels like climbing a wall!

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