Why a 4 to 1 TUR is Not Enough: The Importance of Analyzing the Probability of False Accept Risk: Several organizations and publications reference or insist on maintaining a 4 to 1 TUR (Test Uncertainty Ratio) without understanding the level of risk that they may be subjecting themselves to. The general thought is that if the lab performing the calibrations has standards at least four times better than what they are calibrating, everything will be good. This paper discusses TUR, PFA Risk, and why the location of the measurement matters. We will discuss two managed risk guard banding methods (5 & 6) in the ANSI/NCSL Z540.3 Handbook. We will show that a 4 to 1 TUR is insufficient and can result in a 50 % risk. Check out our blog post on TUR here.
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