If You Do Not Have Uncertainty, You Do Not Have a Calibration: A Guide to Calibration Measurement Uncertainty A Price Tag That Just Says "Some" You take your truck to the shop. The mechanic looks under the hood and says the repair will cost "some." You ask how much is some. He shrugs and hands […]
Where One Term Ends and the Next Begins, Decision Rules FAQ - Quick Answers on TUR, Guardbands, and Risk ("Part 8") Seven parts generate questions. Here are the ones that show up most, with short answers and a pointer to the part that carries the long version. It’s also the credits section, hence part 8 […]
Where One Term Ends and the Next Begins, Part 7 of 7: PFA and PFR Explained: Probability of False Accept and Reject A kicker makes 97 % of his field goals from the 35-yard line. This kick is from the 35, and it sails wide. Based on the population data alone, you would have said it […]
Where One Term Ends and the Next Begins, Part 6 of 7: Guardband Calculation Ask a field goal kicker about the wind. The goal posts never move. But a kicker facing a strong crosswind aims inside the upright to compensate for the drift he knows is coming. That aim point is the acceptance limit. The […]
Where One Term Ends and the Next Begins, Part 5 of 7: Decision Rule Selection - Which Rule to Use and When "Would you tell me, please, which way I ought to go from here?" Alice asks the Cheshire Cat. "That depends a good deal on where you want to get to," the Cat says. […]
Where One Term Ends and the Next Begins, Part 4 of 7: Test Uncertainty Ratio (TUR) - A Screen, Not a Decision Rule Figure 7. Consumer risk against accuracy ratio. The curve passes through roughly 1 % consumer risk near a 3:1 ratio, the relationship Hayes worked on. Jerry Hayes of the United States […]
Where One Term Ends and the Next Begins, Part 3 of 7: Bias vs Uncertainty - Why Compensation Is Not Padding Picture two bathroom scales. The first reads 2 lb heavy every single time, dead consistent. The second is perfectly centered on average but jumps around by a pound either way. The first scale has a […]
Where One Term Ends and the Next Begins, Part 2 of 7: CMC vs Measurement Uncertainty: The Number on Your Certificate Pull up any accredited lab's scope of accreditation, and you will find a line for force: perhaps 0.002 % of applied, or 0.025 % of applied, or 0.05 % of applied. Many people read that line and […]
Where One Term Ends and the Next Begins A Seven-Part Series on Measurement Uncertainty, CMC, Bias, TUR, Decision Rules, Guardbands, and PFA/PFR A customer or someone who I hope is a friend wrote to me with a suggestion. There is a messy mix of terms in conformity assessment, and no single place that says where […]
Obsolete Units of Measurement: Gone but Not Forgotten On May 20, 2019, a small cylinder of platinum and iridium sitting in a vault outside Paris was let go, kind of. No severance. No farewell lunch. It had defined mass for the entire planet for 130 years, and it found out it was redundant the way most […]
RSS vs. Welch–Satterthwaite: What Your Coverage Factor Is Really Promising Ask ten calibration labs how they combine an uncertainty budget, and nine will say "RSS." Ask the same ten how they pick the coverage factor, and most will say "k = 2, for 95 %." The confidence in that nine out of ten is 90 […]
The GUM in Plain English, Part 7 of 7: Uncertainty Budget: Report It So a Stranger Can Check You Six parts in, we have an expanded uncertainty we can defend: U = 1.71 lbf, k = 2.57, approximately 95 % confidence. This last part covers what most certificates get wrong, reporting it, and then puts […]
