Actually, since the demise of the slide rule I have to do all of my calculations beyond 20 using pieces of knotted string, but I now have so many pieces of knotted string that my calculatin' gets confused sometimes. Just the other day I misread a knot and used 3000 kg. of slurry to toss a golf green -- I was upset, bu cheered by the golfers because they now CANNOT miss the 8th hole.