[QUOTE] Boggle! Yes, your numbers are correct when rounded off, but instead of remembering approximations, why not remember a few points that are exact, since it's no less trouble than remembering approximations? The ones I favor are: 20 = 68 (thank you Kodak) 10 = 50 0 = 32 -40 = -40 etc.[/QUOTE] It is remarkably simple. The whole world works in C whereas the merkins don't. I was brought up with F but had to convert later in life and these days have no problems when thinking down to their level.