So I raced my first enduro this past weekend. I did really well, mostly because the guys on my line had a computer which helped me to zero 6 of 10 checks . The test sections were all me, though Anyway, following the roll chart was a bit difficult. It tells me the speed average and the distance, leaving me to make time calculations on the fly. Not so hard on the road with relatively low averages, but nearly impossible in the woods, especially with the really small print (I do race 40+, afterall). So I thought I would make my own roll chart and add a column for time. Of course, this doesn't really help at secret checks, but if I can stay on time at the other landmarks, I should be pretty close. Knowing the speed average and the distance should make it easy to calculate, but when using a time formatted cell, I can't figure out how much to add to increase the time by one second without accumulating errors to throw it off as time/mileage increases. For example, if the speed average is 24mph, it's 150 seconds per mile. With a key time of 8:00:00, my watch should read 8:02:30 at the 1-mile mark, 8:05:00 at the 2-mile mark, and 9:20:29 at the 32.19 mile mark. But adding a number equal to my speed average in seconds per mile times the distance in miles (150 s/m x 2 miles = 300 seconds or 5 minutes) doesn't increase a time-formatted cell in 1-second increments (or one minute, hour or day increments). So I need to figure out what number increases the time by exactly 1 second and then use that number to convert my speed average so it works out, but that number always seems to have a decimal in it, causing the accumulated error. Or maybe I need to time-format my speed average figure , or is it something else? Sure, I could just buy an enduro computer, but I kinda feel like that's cheating and I'd really like to at least try to do it my way. So if anyone can help me, I'd really appreciate it.