Now we're talking about something I actually understand--statistics. All of the factors Al mentions here are classified as error. They are random variances with a mean of zero, so they can be disregarded. For instance, on a long ride, you will go uphill, and then downhill, then uphill, then downhill. It all averages out in the end, so you don't even have to think about it. (In fact--if you start riding at home, and finish at home, you must ascend and descend equal distances. It is impossible to do otherwise.)Originally Posted by noisebeam
Other variables are similar. Sometimes your tires are soft, sometimes they're overinflated, but it all evens out so you don't have to measure it. Same with wind, temperature, your general physical condition, etc. The only factors you have to worry about are those which have a consistent effect on whatever you are trying to change or measure. These factors are called independent variables.
This means that Al's point is correct and the program mentioned by Yontman is unnecessarily complex, since it confuses error terms for independent variables. The simple Internet calculators mentioned by Al and simco are probably better tools.