> Or just punch the PI button on the calculator. I'm not going to do > 355/113 > without a calculator, and if I've got one I don't need 355/113. For some values of calculator :-). Often enough the calculators I find in my hand when I want to use Pi thereon don't have a Pi key. As I have Pi memorised to more places than that approximation gives it's not an issue for me, but for many people it's potentially useful. I always carry a 4 function calculator with square root (which most calculators have these days) plus a single memory. I carry this one because it has a hard shell (essential if it is going to survive me for more than a week), and a large display for it's size and a reasonably good keyboard. Occasionally I feel the need to calculate the log of a number - usually to base 10. Most people find they can overcome such urges but I sometimes succumb. A usable approximation for log 10 is [where S = sqrt] Enter number SSSSSSSSSSS -1 = x 889 = Voila / QED. The first '=' is used to force correct arithmetic precedence as some calculators trip up on this. You can take more or less sqrts and adjust the constant. I have found that 11 x sqrt is a best compromise for accuracy. With infinite precision the more sqrts the better but due to lsd drop off 11 is usually about right. About 3 parts in 10,000 inaccuracy. I leave the reason that this works as an exercise for the student (except Olin, who doesn't need it :-) ). FWIW - if you remember a very few logs to about 4 digits you can derive enough others to do a creditably good job of taking the log of most numbers - enough so that you can perhaps do it in your head while clinging to the side of a precipice (oe elsewhere), when using a hand to access your calculator is liable to be life threatening. Whether you ever would want to will depend on how deeply engrained engineeringness is in uour psyche. RM -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist