Weren't we all. Most scientific calculators have a "pi" key, but if you are forced to use a simple calculator, 355/113 is a good enough approximation for virtually any engineering work (better than 0.1 ppm). Write it as a classic long division problem and you will never forget it.
Much less mnemonic, but 104348/33215 agrees with the pi key on my 10 digit calculator. If I subtract them, the calculator gives zero. ________________________________ From: Pat Naughtin <[email protected]> To: U.S. Metric Association <[email protected]> Sent: Sun, May 29, 2011 6:45:54 AM Subject: [USMA:50533] Value of pi On a more serious note, I was brought up in my early education to believe that pi was equal to 22/7 and that all circles had a radius that was a multiple or sub-multiple of 7. These days, if I want a quick value for a circular area I use diameter squared multiplied by 0.8, where 0.8 is an approximation of pi/4 (pi/4 = 0.7854). As an example, my garden rainwater tank is 3 metres in diameter and it is 2 metres up to the overflow pipe. My estimate of its volume, done in my head, goes something like this: 3 metres squared = 9 square metres. 9 square metres times 0.8 = 7.2 square metres = area of the base of the tank (say) 7 square metres. 7 square metres times 2 = 14 cubic metres or 14 000 litres. When I bought this tank it was specified to hold 13 500 litres so it looks like I got a good deal. Cheers, Pat Naughtin Geelong Australia ________________________________
