Guard Banding Definitions

There are a number of Guard Banding methods that are available depending on the standards document.  Transcat has standardized on the methods shown below.  Each method is briefly explained with the formulas and options shown in the chart below.  You do have the option of a custom guard band method.  If you have questions or need further assistance, please speak with one of our calibration specialists at 800-828-1470 or complete our simple contact us form.

• ASME B89.7.3.1 Simple Acceptance: Simple Acceptance Using a 4:1 Ratio with Mean Measurement Results and Rejection with Cause
• ANSI/NCSL Z540.3: 2006 Method 5: If the measurement result is within such acceptance limits, the PFA is very small and is therefore assured of meeting the 2 % PFA requirement. The only information necessary for this guard banding approach is the tolerance and the calibration process measurement uncertainty.
• ANSI/NCSL Z540.3: 2006 Method 6: Applying a guard band based on this maximum PFA value and the corresponding TUR ensures that the PFA is 2 % or less regardless of the in-tolerance probability.
• ILAC-G8:2019 [4]: Pass/Fail criteria uses the 95 % expanded uncertainty for making statements of conformance. For measured values where the specified tolerance is within the 95 % expanded uncertainty interval, no declaration of conformance is made. Most European accreditation bodies require ILAC-G8 for statements of conformance for ISO/IEC 17025 calibrations
• ASME B89.7.3.1 Clause 5.2 Stringent Acceptance: Stringent acceptance and relaxed rejection using symmetric 100% two-sided guard bands with mean measurement results and rejection with cause.
• ASME B89.7.3.1 Clause 5.3 Relaxed Acceptance: Relaxed acceptance and stringent rejection using symmetric 100% two-sided guard bands with mean measurement results and rejection with cause.

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