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 […]
The GUM in Plain English, Part 6 of 7: Coverage Factor: Why k = 2 Sometimes Lies Part 5 combined our nine inputs into a combined standard uncertainty of uc = 0.666 lbf. That is one sigma, and by itself, it is too thin to act on. Figure 11. One sigma catches about 68 %. […]
The GUM in Plain English, Part 5 of 7: Combined Standard Uncertainty: The Catch Called Correlation Parts 3 and 4 sized all nine inputs in our 5000 lbf budget: four Type A pieces earned from data, five Type B pieces built from what we already knew. Now you need one number for the result. You […]
The GUM in Plain English, Part 4 of 7: Type B Uncertainty: The Doubt You Already Know Part 3 earned four numbers by repeating measurements: our Type A pieces, led by a 0.58 lbf single-reading repeatability at 3 degrees of freedom. But not all doubt comes from repeating a measurement. Most of it, in a […]
Part 3 of 7: Type A Uncertainty: The Doubt Your Own Data Hands You In Part 2 we wrote the measurement model and named every input in our 5000 lbf budget. Now we start filling in numbers, beginning with the ones we earn ourselves. Figure 4. Four loadings at 5000 lbf: 5000, 5001, 5000, 5001. […]
The GUM in Plain English, Part 2 of 7: Error vs Uncertainty, and the Exhaust Port in Your Model In Part 1 we agreed that a measurement without an uncertainty is an opinion with a decimal point, and we listed where the doubt in a force lab comes from. Before we can size any of […]
Part 1 of 7: Measurement Uncertainty: An Opinion With a Decimal Point Pull any calibration certificate off the shelf, and you will find a line like U = 1.71 lbf, k = 2.57, approximately 95 % confidence. Most of the people who read that line, including some who sign it, could not tell you where […]
Required Reading: Good to Great Leadership Lessons for Calibration Labs “Good is the enemy of great.” Jim Collins, Good to Great: Why Some Companies Make the Leap and Others Don’t Most companies want to be good. Most calibration laboratories think they are good; some are not, and people can feel free to comment on horror […]
Same Data, Four Answers: What the JCGM’s New Torque Example Teaches Us About Calibration Curve Fitting Eight torque points. One straight line. Four defensible answers. Figure 1A close-up of a torque cell being used in a Morehouse torque transfer machine That is the punchline of Example 9 in JCGM GUM-5:2026, the new examples volume in […]
JCGM GUM-5:2026 Has a Force Example in It! The Scatter Was Never the Story: The JCGM’s Breaking-Force Example and What Really Drives Force Uncertainty Steel wire rope used for hoisting in vertical mine shafts. Source: JCGM GUM-5:2026, Example 15, clauses 15.1–15.6. Thousands of workers ride steel wire rope down mine shafts every day, which is […]
