This estimator is based of Naismith's rule for estimating walk time and adapted with Langmuir's rule for descent. The rule estimates walk times from point a to b while allowing for elevation change. This equation builds on the fact that Time = Distance/Speed and factors elevation change @ +1hour for every 2000' in ascent and 0.75 hour for every 1640' descended.
Using the estimator
Distance: the length of your trip
Walking speed: Your speed of travel. Factor the speed of the slowest member of your party. this number should be between 1-4mph ranging from athletic to less athletic.
Climb and Decent: These are numbers dealing with your elevation change. Starting at 100' and ending at 1500' you would have an elevation change of 1400'. If that trip is in and out 1400 would be both numbers.