This turns out to be way too complex for me. I figure, long portages take longer than short portages. Of course, if I've been across a trail before, I have a pretty good idea. But things change. Consider, for example, the change from the south side of Kashashapiwi after the beaver dam got removed. Before I got there, I knew the dam was gone and could take that into account. But suppose you get somewhere and did not know of a change in the trail? Yet, I guess science can be applied to whatever.

Tim