Walker's Self Computing Lumber Scale is a simple but invaluable tool that tells you instantly the number of joists, studs, rafters, wall furing, and floor strips you need. It automatically includes an extra piece for the end of a section. There are scales for 12'', 13.8'', 16'', 19.2'' and 24'' on center spacing. One side of the scale works on 1/4'' scale plans, and the other side is for 1/8'' scale.
Walker's Self Computing Lumber Scales are white plastic, 1-1/8'' wide by 6-1/4'' long (folds out to 12-1/2'' long), so it fits conveniently in your pocket.