What you need to know about Z540 and Calibration.





ANSI Z540.3 - Requirements for the Calibration of Measuring and Test Equipment- offers very specific guidance for a proper calibration program.  

Here is what you need to know


Z540.3 and Calibration.


  • Test Uncertainty Ratio- Section 3.11 provides a definition of TUR.  Look at your boilerplate RFQ for calibration.  Our experience is that it is still common practice to see TAR- Test Accuracy Ratio of 4:1 called out in the terms. You really need to understand what you are asking. You may want to read TUR:What is it?


  • Clear Objectives for Your Calibration Program- Section 4.1 requires that you "establish, document, operate and improve" your calibration program. The basis for your calibration can be customer requirements, legal or regulatory or experiential based. The bottom line is you need to use a well articulated thought process for why you calibrate something.

  • Clear Identification of Equipment- Section 5.2.1 calls out the need for unambiguous identification of equipment and calibration status. While a calibration sticker is not required, there must be some method that clearly identifies the equipment and calibration status. 

  • Defined Calibration Intervals- Section 5.4.1 requires the end user not the calibration company  to define the calibration interval. In addition, the calibration needs to be based onZ540.3 and calibration.jpeg a review of data. Simply stating 6 months without relevant data to support that decision is not good enough. NCSLI provides an excellent resource -RP-1: Establishment and Adjustment of Calibration Intervals.


  • As Found Data- Section requires the end user to look at the data BEFORE adjustment(if any) and make a determination as to the impact on product quality.

  • Calibration System Audit- Section 6.2 requires an independent audit of the calibration system and these audits must be documented.

Download our FREE Calibration Audit Checklist

  • Select a competent calibration provider- Section 5.3 specifically mentions ISO 17025 accreditation as a measure of competence.

As  an 17025 accredited provider of calibration services conflict arises when those unfamiliar with ANSI Z540.3 ask us to make decisions that must be made by the end user. As the end user of the calibration equipment you need to have an open dialogue with your calibration provider. 

While we did not cover everything about Z540.3 and calibration we hope this will assist you in having a better informed conversation with your calibration provider.

We would love to hear your questions.  Please feel free to comment below.


Visit our International Standards used in Calibration page for more on standards used in calibration.


Phil Wiseman

Phil Wiseman

Phil Wiseman is Chief Marketing Officer at Alliance Calibration. He earned a B.S. in Chemical Physics from Centre College. Phil is an ASQ Certified Quality Auditor and ASQ Certified Manager of Quality/Organizational Excellence.

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