--- title: "Traceability and hierarchy of standards" subject: "Metrology" chapter: 3 key: "semester_3/metrology:traceability-hierarchy-of-standards" source: https://www.bctengineer.com/q/semester_3/metrology/traceability-hierarchy-of-standards site: BCT Engineering --- # Traceability and hierarchy of standards Metrology · Chapter 3: Standards, Standardization, Standardizing Organizations - Asked in: year not given, 8 marks - Video: [Introduction to Metrology: Measurements, BIPM, SI, traceability, calibration and standards](https://www.youtube.com/watch?v=Pn7VHO1LOAw) — Israel Cayetano - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/metrology/traceability-hierarchy-of-standards - Whole chapter: https://www.bctengineer.com/md/semester_3/metrology/chapter-3 ## Question Explain traceability of measurement. Describe the hierarchy of standards from the international prototype to the workshop gauge, and classify standards of measurement. ## Answer **Traceability** is the property of a measurement result by which it can be related to national or international standards through an unbroken chain of comparisons, each with a stated uncertainty. It assures that a reading taken in a workshop agrees with readings taken elsewhere. #### Classification of standards | Standard | Use | |---|---| | Primary | Realises the unit with the highest accuracy; kept at the national laboratory, used only to calibrate secondary standards | | Secondary | Calibrated against the primary standard; reference for the calibration laboratories | | Tertiary | Reference standard of an industry or calibration lab, used to calibrate working standards | | Working | Used daily in the workshop for inspection and for calibration of gauges and instruments | Standards may also be classified as *line standards* (length between two lines, such as the old metre bar), *end standards* (distance between two flat faces, such as slip gauges) and *wavelength standards* (based on the wavelength of light). #### Hierarchy ```text International standard (BIPM) | National standard (national lab) | Accredited calibration laboratory (secondary / reference standard) | Company reference standard (master slip gauge set) | Working standards (workshop gauges) | Inspection of the product ``` Accuracy decreases by a factor of about 3 to 10 at each step, and each step is documented by a calibration certificate. For length, the unit is now defined by the speed of light: the metre is the distance travelled by light in vacuum in $1/299\,792\,458$ s. #### Importance Traceability ensures interchangeability of parts made in different places, gives confidence to customers, and is required by quality systems such as ISO 9001 and ISO/IEC 17025. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Traceability of a measurement means the result can be related to national or international standards through: A. A single comparison with a master gauge B. An unbroken chain of comparisons, each with stated uncertainty C. The use of the most expensive instrument D. Repeating the measurement many times Answer: B. Traceability requires an unbroken chain of comparisons with stated uncertainties, assuring agreement of readings everywhere. (Key point: Traceability definition) 2. What is the role of a primary standard? A. Daily inspection in the workshop B. Calibration of workshop gauges directly C. Realise the unit at the highest accuracy and calibrate secondary standards only D. Reference for company master gauges only Answer: C. The primary standard is kept at the national laboratory and is used only to calibrate secondary standards. (Key point: Primary standard) 3. Which is the correct order from top to bottom of the hierarchy? A. National lab, international (BIPM), calibration lab, workshop gauges B. Workshop gauges, company reference, calibration lab, national lab C. International (BIPM), national lab, accredited calibration lab, company reference, working standards D. International (BIPM), company reference, national lab, working standards Answer: C. The chain goes BIPM, national lab, accredited calibration lab, company reference standard, working standards, product inspection. (Key point: Hierarchy order) 4. As one goes down the hierarchy of standards, accuracy: A. Increases by a factor of 3 to 10 at each step B. Stays the same C. Decreases by a factor of about 3 to 10 at each step D. Becomes unimportant Answer: C. Each step down loses accuracy by about 3 to 10 times, and each step is documented by a calibration certificate. (Key point: Accuracy down the chain) 5. Slip gauges are an example of which type of standard? A. Line standard B. End standard C. Wavelength standard D. Primary standard Answer: B. End standards give length as the distance between two flat faces, as in slip gauges; line standards use two lines, like the old metre bar. 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