“Cumulative Sums of the Poisson” – affectionately called the “Thorndike Chart”

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An old Nomograph that can save Risk Analysts and Reliability Engineers a lot of time: “Cumulative Sums of the Poisson” – affectionately called the “Thorndike Chart”

If you ever had to explain to a customer that the expected number of “catastrophic” events over the next (say) 10 years is a small fraction < 1. ..(say 0.26 events).. Using the Thorndike chart you can see that using µ=0.26, the Probability of seeing 1 (or more) events over the same time period is 0.24. Much easier to explain to a customer than 0.26 “expected” events!! Thorndike Chart

Previously published in the June 2013 Volume 4, Issue 2 ASQ Reliability Division Newsletter

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