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Appendix M Estimating the Accuracy and Precision of the Digital Caliper and Faro Laser
Pages 323-340

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From page 323... ... As discussed in Chapter 5 and Appendix G, both accuracy and precision are important characteristics in determining the suitability of a measurement system for use in a testing process. During Phase III, two new data sets were presented to the committee: the side-by-side comparisons of BFD measurements made by the Aberdeen Test Center (ATC) Read the entire page →
From page 324... ... Consider first the question of relative accuracy. For the ATC data, the average difference between the laser and caliper measurements is 1.36 mm. Read the entire page →
From page 325... ... . For the Chesapeake Testing data, the average difference between the laser and caliper is 1.56 mm, with a 95 percent confidence interval of (0.98, 2.13) Read the entire page →
From page 326... ... mm. The estimate of the variance of the laser is 1.09; the precision (standard deviation) Read the entire page →
From page 327... ... (2008) , estimated the precision of the Faro laser as 0.0970 mm:  laser combined standard uncertainty   laser operator   laser error   laser instrument spec ˆ ˆ2 ˆ2 ˆ2  0.04102  0.08172  0.03252  0.0970 The data contain information only about the variation in the operator and the error. Read the entire page →
From page 328... ... (2008) , estimated the precision of the caliper as 0.823 mm:  caliper combined standard uncertainty   caliper operator   caliper error   caliper instrument spec   correction factor ˆ ˆ2 ˆ2 ˆ2 ˆ2  0.47152  0.362  0.00732  0.57 2  0.823, Because the data contain information only about the variation in the operator and the error, the "statistical uncertainty" corresponds to the first two terms. Read the entire page →
From page 329... ... However, calculating confidence intervals for precision and accuracy takes into account both sample size and design differences. 76 Rick Sayre, Deputy Director, OSD DOT&E Live Fire Test and Evaluation, and Tracy Sheppard, Executive Officer & Staff Specialist, OSD DOT&E, "DoD In Brief to the National Research Council Study Team," presentation to the committee, November 30, 2009. Read the entire page →
From page 330... ... (2008) derived the 0.57 mm uncertainty associated with the postmeasurement correction using the delta method, a standard statistical approach for estimating the variance of complicated statistics -- in this case, the variability for the correction factor. Read the entire page →
From page 331... ... So, while intuition would suggest that smaller magnitude offsets result in improved caliper precision, using the offset mean and standard deviations from the ATC data, which has a smaller mean offset but a larger standard deviation, results in a larger uncertainty estimate. Measurements in Walton et al. Read the entire page →
From page 332... ... So, as long as the precision of the measuring instrument is less than onetenth of the variation in the actual BFDs, the measurement instrument only negligibly increases the variation in the observed BFD, where "negligible" is defined as ≤ 0.005. For the current clay process with an observed BFD standard deviation of 3.5-4.5 mm or so, this means the precision of the measuring instrument, in terms of its standard deviation, should be no greater than 0.3 to 0.4 mm. Read the entire page →
From page 333... ... 08-MS-25. Aberdeen Proving Ground, Md.: Aberdeen Test Center Warfighter Directorate, Applied Science Test Division, Materials and Standards Testing Team. Read the entire page →
From page 334... ... PREPUBLICATION DRAFT -- SUBJECT TO EDITORIAL CORRECTION TABLE M-1 Side-by-Side Comparison of BFD Measurements by ATC   Laser Arm, Data Digital Smoothed (mm) Number Caliper (mm) Read the entire page →
From page 336... ... PREPUBLICATION DRAFT -- SUBJECT TO EDITORIAL CORRECTION TABLE M-2 Side-by-Side Comparison of BFD Measurements by Chesapeake Testing BFD Digital Faro Data Caliper Laser Number (mm) Read the entire page →
From page 338... ... PREPUBLICATION DRAFT -- SUBJECT TO EDITORIAL CORRECTION 70 33.8 35.5 71 35.4 37.1 72 41 40.4 73 33.6 34.7 74 36.2 37.9 75 33.6 35.3 76 35.5 44.6 77 55 55.2 78 34.2 37.8 79 33.1 33.7 80 36 37.7 81 35.4 36.1 82 33.5 37.5 83 36.1 37 TABLE M-3 Faro Data Impression (j) O perator (i) Read the entire page →
From page 339... ... PREPUBLICATION DRAFT -- SUBJECT TO EDITORIAL CORRECTION TABLE M-4 Caliper Data Impression (j) Operator (i) Read the entire page →

From page 323...

... As discussed in Chapter 5 and Appendix G, both accuracy and precision are important characteristics in determining the suitability of a measurement system for use in a testing process. During Phase III, two new data sets were presented to the committee: the side-by-side comparisons of BFD measurements made by the Aberdeen Test Center (ATC)

Appendix M Estimating the Accuracy and Precision of the Digital Caliper and Faro Laser Pages 323-340

Appendix M Estimating the Accuracy and Precision of the Digital Caliper and Faro Laser
Pages 323-340