Started wondering about this when I was going up a sneaky little rise that looks flat (or even downhill) but gets heavier and heavier on the legs. I mean, that's not a hill. And then on the way home, there's a long, gentle incline alongside teh park - but you can spin up it with no bother so that can't be a hill. Later on, there is a slope in 2 parts which I reckon would be a hill, if it wasn't for flat bit linking them that gives you a rest. So when does it start to count?