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articles:what_are_accuracy_ratios [2023/05/14 12:39] – rrandallarticles:what_are_accuracy_ratios [2023/05/14 21:33] (current) – rrandall
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 ====== What are Accuracy Ratios ====== ====== What are Accuracy Ratios ======
 +{{keywords>accuracy ratio}}
 Many users overlook the requirement in both ISO 9001 & AS9100D that states:  Many users overlook the requirement in both ISO 9001 & AS9100D that states: 
 <blockquote>7.1.5 Monitoring and measuring resources \\ 7.1.5.1 General \\  <blockquote>7.1.5 Monitoring and measuring resources \\ 7.1.5.1 General \\ 
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 <WRAP centeralign>**Dimension tolerance being measured ÷ Accuracy of measuring device used = Accuracy Ratio** </WRAP> <WRAP centeralign>**Dimension tolerance being measured ÷ Accuracy of measuring device used = Accuracy Ratio** </WRAP>
 <WRAP clear></WRAP> <WRAP clear></WRAP>
 +{{ :articles:micrometer-pngrepo-com.png?direct&60|Source: https://www.pngrepo.com/svg/234351/micrometer}}
 Using another example, let's assume that you have a micrometer with an accuracy of ±0.0001". And you're using it to measure a dimensional feature with a tolerance of ±0.005". Divide 0.005 by 0.0001 to obtain your accuracy ratio. In this scenario, you'd have an accuracy ratio of 50:1. Using another example, let's assume that you have a micrometer with an accuracy of ±0.0001". And you're using it to measure a dimensional feature with a tolerance of ±0.005". Divide 0.005 by 0.0001 to obtain your accuracy ratio. In this scenario, you'd have an accuracy ratio of 50:1.
  
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 However, if the dimensional feature had a tolerance of ±0.001", and was measured using an instrument accurate to ±0.00015". Multiply that instrument accuracy (0.00015") by 2. Then determine your new accuracy ratio using the calculation of 0.001 ÷ 0.0003, which results in a new accuracy ratio of 3.3:1. Since this accuracy ratio is below 4:1, then this would reveal an increased likelihood that nonconforming product had been delivered to the customer. However, if the dimensional feature had a tolerance of ±0.001", and was measured using an instrument accurate to ±0.00015". Multiply that instrument accuracy (0.00015") by 2. Then determine your new accuracy ratio using the calculation of 0.001 ÷ 0.0003, which results in a new accuracy ratio of 3.3:1. Since this accuracy ratio is below 4:1, then this would reveal an increased likelihood that nonconforming product had been delivered to the customer.
 +
 +===== Out-of-Tolerance Impact Analysis =====
 +
 +Many users also overlook the requirement in both ISO 9001 & AS9100D that states: 
 +<blockquote>7.1.5.2 Measurement traceability \\ 
 +//The organization shall determine if the validity of previous measurement results has been adversely affected when measuring equipment is found to be unfit for its intended purpose, and shall take appropriate action as necessary.//</blockquote>
 +
 +The best, and easiest way to "//determine if the validity of previous measurement results//" is to, as described above, calculate the "accuracy ratio" based on the results ("As Found" condition) reported by the Calibration Lab.
 +
 +If the diminished "Accuracy Ratio" remained above 4:1, then there is a reasonable degree of confidence that the OOT (Out-of-Tolerance) condition did not "adversely" affect the delivered product or service. However, if the diminished "Accuracy Ratio" fell below 4:1, then there is a reasonable degree of uncertainty in whether the OOT (Out-of-Tolerance) condition "adversely" affected the delivered product or service. And the lower the "Accuracy Ratio" (<4:1), the greater the probability that the delivered product or service had been "adversely" affected.