What TUR Do You Really Need ? Putting Statistical Theory into Practice

The ageless question in metrology is, “What Test Uncertainty Ratio (TUR) is required to properly calibrate an instrument?” Numerous papers on guardbanding and statistical techniques have been published to address this question. Most recently, these discussions have focused on the very conservative “in-tolerance” conditions proposed by ISO Guide 25, draft 5. Although ISO Guide 25 is being replaced by ISO 17025, and the present draft (DIS 17025) does not have the strict guardbanding requirements, the draft 5 proposal presented a perspective that has merit. [1][2] The philosophies of other guardbanding methods have also been discussed in detail, especially by Dave Deaver of the Fluke Corporation. [3][4][5]