> Then there are 'grades,' used on roads and probably elsewhere. For example, occasionally one sees signs warning of "6% grade next 10 miles" or something similar. What is grade?
>


I've always thought that this refrred to a percentage of vertical, i.e. 90 degrees. "6% next 10 miles" would thus mean an average angle of 5.4 degrees relative to horizontal. This corresponds to a total drop (or increase) of umm..., (calculator, calculator) ... 10 miles x 1609 metres per mile x 0.06 = 965,4 metres.

180-90-5.4=84.6 degrees (ok, so it's not quite to scale)
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jul"just a driver"ian