Can anyone tell me if the percent of a grade is measured using the horizontal distance or the running distance? I know it doesn't make a measurable difference on usual RR grades, but Mt Washington cog has a 37% grade and that might make a difference. I also read a reference where straight up and down was 100%.

It's horizontal distance. Picture a right triangle. The hypotenuse (sp?) is the running distance, the other two legs are the horizontal and the vertical distances. Grade in percent = V*100/H. Straight up would mean that H is 0, so the grade would be infinity, not 100%! If V=H, i.e a 45 degree climb, then the grade would be 100%. You're right that it normally makes little or no difference whether you use the horizontal or the running distance, only if you're talking ridiculous grades like 37%. Bill