a cup's weight depends on the time you hold it.

This is, indeed, a bugger of a calculation. However, we are lucky because rate of water evaporation isn't determined using weight. It seems like taking Arizona as a reasonable examine would do, where a general evaporation rate of a third of an inch per day is estimated, which would mean a week or so.Since I don't think we have a volunteer that wants to stand around looking silly, you can also just leave a glass of water somewhere and see.Btw, without mucking about too much with determining the surface area of a paper cup, I'd say about 1.4 grams per hour in evaporation without heating...This message has been edited by Melchior, 07-20-2004 11:30 PM