On 16 May 1924, ninety years ago today, Walter Shewhart sent his manager a short memo, no longer than one page. Shewhart described what came to be called the control chart, what we would today call a process behaviour chart.
Shewhart, a physicist by training and engineer by avocation, had been involved in improving the reliability of radio and telegraph hardware for the Western Electric Company. Equipment buried underground was often costly to repair and maintain. Shewhart had realised that the key to reliability improvement was reduction in manufactured product variation. If variation could, hypothetically, be eliminated then everything would work or everything would fail. If everything failed it would soon be fixed. Variability confounded improvement efforts.
Shewhart shared a profound insight about variation with a diverse group of independent contemporaries including Bruno de Finetti and W E Johnson. If we wanted to be able to reduce variation, we had to be able to predict it. Working to reduce variation turned on the ability to predict future behaviour.
De Finetti and Johnson were philosophers who didn’t go as far as turning their ideas into instrumental tools. The control chart turned out to be the silver bullet for predicting the future. It is a convivial tool. Shewhart invented it ninety years ago today.
If it isn’t supporting and guiding your predictions, you’re ninety years out of date (assuming that you’re reading today).
See the RearView tab at the top of the page for further background.