Expedition: general discussions.

So what's the big deal? If such mistakes ruin the mood and the desire to play (or if there wasn't much desire to begin with), that's one thing. But if that's not the case, you can just take a time-out, recalculate, it's not that hard.
As for the mechanic – if it turned out to be complex and unsuccessful, it's worth either passing it on to someone else, or writing a program like Shaman did to make the calculations easier, or just not bother with it at all. IMHO.