Six Sigma

You don't need to know, but in case you want to.... It is do do with normal curves. Let's say an engineering company has to cut a piece of metal to a particular size. The actual length will vary slightly, with a particular standard deviation (sigma) following a normal distribution. By the time you have moved 6 standard deviations from the mean (6 sigmas), the chance of an item's length beyond that is very small. Six sigma would claim that 99.99966% of results will be within that tolerance, so almost flaw-free production.