I have also wondered this for quite a while........i understand the "altitude gained" part of the equation, but is the "distance covered"=distance on the road, or horizontal distance?

I have also wondered this for quite a while........i understand the "altitude gained" part of the equation, but is the "distance covered"=distance on the road, or horizontal distance?

Formula for gradient = dy/dx ; which are perpendicular measurements,
therefore:
gradient equals (change in vertical height) divided by (change in horizontal distance).

But it doesn't really make that much difference for small angles like 10%. See what I mean by drawing a 90° triangle with a 10cm horizontal base and 1cm vertical height. Measure the hypotenuese (diagonal) and compare it to the 10cm base.