2014: Advent Quality: Free-Range Widgets

by on December 14, 2014

How narrowly a range should be defined depends entirely on what you’re making and what its purpose is. Red paint for car repairs needs to be very exact in shade, but the levels of bacteria are probably completely irrelevant. Red icing for cakes needs to be recognisably close in shade to past batches of those cakes, but the human eye is much better at spotting a difference in colour when things are right next to each other than remembering a slight difference, and natural variation in cake colour is probably okay even if someone did notice it – but the bacteria count must be below specific levels.

How narrowly your range can be usefully defined also depends on your measuring equipment., It’s not unreasonable to define something as “below 5 ppm”, for instance, if levels below 5 ppm cannot be detected. If you define your range as “below 4 ppm” and you can only measure numbers greature than 5 ppm, everything is going to fail, because you won’t be able to tell whether it ought to pass.

This is another of those subtle arts. Defining your limits too widely will result in widgets that are not fit for use or, worse, look fit for sale but turn out not to be safe. Defining your limits too narrowly, though, can cause you serious problems too.

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