The following are some of the reasons why we need to have traceability in our calibration:

1. It is a necessity in calibration, you cannot call it calibration if the reference standards are not traceable to SI.

2. It is a requirement of standards like ISO 17025 and ISO 9001.

1. Clause 7.1.5.2 When measurement traceability is a requirement or is considered by the organization to be an essential part of providing confidence in the validity of measurement results, measuring equipment shall be: a) calibrated or verified, or both, at specified intervals, or prior to use, against measurement standards traceable to international or national measurement standards;

2. Clause 6.5.1 The laboratory shall establish and maintain metrological traceability of its measurement results by means of a documented unbroken chain of calibrations, each contributing to the measurement uncertainty, linking them to an appropriate reference.

3. As per ISO 17025, below are the requirements..

4. For ISO 9001, below are the requirements:

3. For companies engaged in manufacturing and engineering, it ensures that parts produced or supplied have the same or acceptable specifications when used by customers anywhere. Compatibility is not an issue.

4. Traceability provides confidence to our measurement process because it ensures the validity and accuracy of the measurement results.

5. Traceability has a numerical value, this value is displayed in a calibration certificate as the measured value plus the measurement uncertainty results. The smaller the uncertainty results are, the more accurate the measurement instruments.

6. A requirement by relevant laws and regulations to guarantee product safety and quality- even though we have different units of measurements, we are confident that compatibility in terms of size, form or level is not an issue anywhere it goes.

2 Implementation Requirements for Metrological Traceability as Per ISO 17025

In every step or sequence of the Traceability chain where we relate a measurement result to a reference, this process must be under control to ensure that the quality of transferred measurement results are maintained. 

Once the reference standard has left the laboratory where it was calibrated, it is now our responsibility to ensure and maintain the validity of its measurement results.

You may have established the traceability of your reference standard, but during calibration in your lab, the method used is not valid or the person performing the calibration is not properly trained, because of this, there is no confidence in the results, therefore calibration results are compromised.

With all these factors, the unbroken chain of comparison to SI is not enough, we need to implement a measurement assurance program in order to ensure the validity of traceability in the long run.

Going back to the requirements of ISO 17025, where it states: “The laboratory shall establish and maintain metrological traceability of its measurement results by means of a documented unbroken chain of calibrations, each contributing to the measurement uncertainty, linking them to an appropriate reference.”

There are 2 implementation requirements that we must consider in order to satisfy Metrological Traceability, and for us to ‘claim traceability’ in our measurements, these are:

1. Establish Metrological Traceability

2. Maintain Metrological Traceability

Establishing the Traceability Chain 

Establishing traceability is where the technical aspect of traceability, focusing on the reference standards (the calibrators). This is where the actual link to the SI is objectively seen – a traceable standard.

We always read that in order to have a valid calibration, it should be traceable to the International Standard or SI through the unbroken chain of calibration. This unbroken chain of calibration is how we establish this traceability chain.

We can easily establish the traceability chain, we just need to send our reference standard to a higher level lab or to an accredited lab.

Once this traceability chain is established, we expect to see the following evidence to claim our traceability. These are the:

1. The assigned value of calculated uncertainty

2. Environmental Conditions

3. Calibration Methods used

4. Competency of personnel

5. Identification of the reference standards used during calibration.

You already established Metrological Traceability with a traceable standard, but what’s next?

Our job does not end once we establish traceability in calibration, this is just the beginning. The more challenging part now is to maintain our traceability.

Maintaining Metrological Traceability in Calibration

Maintaining traceability is the 2nd implementation requirement, this is traceability evidence referring to the documented quality assurance program of ISO 17025. 

These are:

1. Internal Audit – focusing on traceability evidence making sure processes are in place

2. Method validation and verification – Making sure that the suitability of procedures or methods are for the intended use.

3. Acquiring traceability through:

1. Calibration and Recalibration

2. Use of certified reference materials

3. Use of other calibrated instrumentation

4. Ensuring the validity of results through:

1. PT or ILC

2. Intermediate Checks

In totality, the ISO 17025 is a standard designed with the purpose of establishing and maintaining traceability in either Test or Calibration performed. A laboratory that is accredited under ISO 17025 standard by a reputable accreditation body is said to be conforming, thus, providing a traceable calibration is ensured.