Metrology and measurement: A detailed guide for manufacturers

What is measurement? It’s the sort of question that seems obvious at first, but the more you think about it, the complex you realise it is.

In the simplest terms, measurement is “the quantification of attributes of an object, which can be used to compare other objects or events.” Another definition goes like this: “measurement is to discover the exact size or amount of something.”

Those definitions focus on the purpose of measurement, the result. But measurement is more than a result, it’s also about the process. The techniques and the technology that we use are equally important. Here’s a much more technical definition, that focuses on this other aspect of measurement:

Measurement is the process of experimentally obtaining one of more values that can reasonably be attributed to a quantity together with any other available relevant information (International Bureaux of Weights and Measures 2021).

An integral part of daily life

Measurement is an integral part of everyday life. It means different things in different contexts. Look at your watch, check the speedometer in your car, and you’re taking measurements. In science and engineering, measurement is far more complex involving very specific methods and technology. However we define it, it’s as fundamental to humanity as speech and numbers. In many ways, the history of measurement is the history of humanity itself.

As long as humans have existed, we’ve been measuring things, there is documented evidence going back to Ancient Egypt. The cubit was length of an arm, from the elbow to the tip of the middle finger. It was a measurement that, in its day, served a good purpose. That’s how they built the Great Pyramid but populations grew, so did the need for standardised measurement techniques. The need to make decisions about the environment led early humans to develop ways to measure and quantify the world.

With the expansion of global trade routes, the need became an imperative and on 20 May 1875 a solution was found. The 17 original signatories of the Metre Convention met in Paris and agreed on the first international unit of measure. This put in place the beginnings of the International System of Units (SI). Since then, that system has continued developing and the science of metrology has flourished.

What is metrology?

Metrology is the science of measurement. It offers a framework for establishing techniques and maintaining standards. It ensures measurements are accurate, consistent, and universally understood. To see how broad the study of measurement is, let’s return to the International System of Units or the seven base units (SI).

• Mass – kilograms (kg)
• Length – metres (m)
• Time – seconds (s)
• Electric current – amperes (A)
• Temperature – kelvin (K)
• Luminous intensity – Candelas (cd)
• Amount of a substance – moles (mol)

These form the basis of most widely used system of measurement in the world, the Metric System. That system is coordinated by the International Bureau of Weights and Measures (the BIPM).

Beyond the base units

From those 7 basic units, we can derive many more units of measure, area, volume, velocity, acceleration, density and so on. Today, we define these units according to universal constants. For instance, the metre is: “The length of the path light travels in a vacuum during 1/299792458 of a second.”

The use of universal constants to define units wasn’t always the case. The definitions have changed many times over the years. Up until 2019 the kilogram was the last unit still defined by reference to a physical object. The international prototype kilogram was a cylinder of platinum-iridium alloy. It was kept under 3 separate bell jars and with strict security in the vaults of the International Bureau of Weights and Measures (BIPM) in Paris. Every weight in the world, even the non-metric ones, can be traced back to the original kilogram (or Le grande K).

The problem with physical objects is that they change over time. Even the most inert materials (like platinum-iridium alloy) will degrade. The mass of the Grand K might be different today than when it was first made, and there would be no way of knowing or proving it. Even minor errors or deviations could have serious consequences. Definitions based on unchanging universal constants are not subject to environmental factors. There is minimal “uncertainty”.

Successful measurement depends on a sound understanding of basic metrology concepts.

Key concepts in measurement

Uncertainty

How many decimal places are there on your kitchen scales? How many times can you tap your feet in a second? In theory, units of measurement are infinitely divisible. In practice, there is a limit to what we are capable of.

The accuracy of a measurement needs to fit the purpose of that measurement. If you’re making a cake and the recipe calls for 100g of butter, it doesn’t make a great deal of difference if you use 99.5g or 100.4g. If you’re building an aeroplane, or a medical device, that level of uncertainty isn’t acceptable.

There is always an element of doubt with every measurement, this is what we call uncertainty. Precision is one source of uncertainty. There are different ways uncertainty can affect measurements. Environmental conditions, observer error, methodology, can all introduce uncertainty. The instruments themselves can drift over time, especially in harsh, dusty environments.

For more information on measurement uncertainty, the National Physical Laboratory has this handy guide.

Calibration and certification

We can remove some of this uncertainty by making sure our measurement devices are calibrated and certified. That means comparing one device with another of a higher accuracy and precision. From there, engineers can evaluate and make necessary adjustments to return the device to its original specifications.

Regular calibration helps identify any deviations in the device’s performance over time, ensuring accurate measurements. Maintaining a schedule for regular calibration ensures the longevity and performance of the equipment.

After calibration comes certification. When a recognised professional calibrates a metrology device they will award it a certification which remains valid for a specific period of time, after which the device will need calibration again.

Some devices need more attention than others. Given the negligible mechanical stress that coordinate measuring machines (CMMs) are subject to during their operational life, in many cases this service is a routine performance verification. For portable systems that are regularly moved around, often in harsh environments, calibrations might require more intervention.

Traceability

Calibration involves comparing one device against another more accurate one. But how do we know that the calibration devices are themselves accurate and precise?

The answer to this question is “traceability”. Traceability in metrology refers to the ability to relate individual measurement results to national or international standards. This ensures that measurements are consistent and comparable across different contexts and locations.

Full traceability means having an unbroken chain of calibrations and complete documentation leading to a recognised authority – in the UK, it’s the National Physical Laboratory (NPL).

Accuracy and precision

In the world of advertising, we commonly see the word “precise”. It inspires trust and confidence, yet to metrologists this is not the case. “Precise” does not mean “correct”, and it’s certainly not the same as “accurate”. A measurement could be precise and still be wrong.  

To understand this concept, let’s take the example Pi (3.14159265…). It would be accurate to say that Pi is equal to 3, or 3.1, but it wouldn’t be very precise. In the world of metrology, the word “precise” is more like “detailed” or “specific”.

It would be wildly inaccurate to say that Pi was 5.7252456. However, it would be precise because we’ve given a very specific and detailed answer, albeit wrong.

To write Pi in a way that is both accurate and precise, we need the number to be correct, and given in as much detail as possible, 3.14159265…

The classic example of this is that of a dart board. If you throw a dart at a dart board and it hits, anywhere on the dart board, that’s accurate but not precise. One time it might be top left, the next time it might be bottom right. As long as you hit the dart board, you’re accurate. If you throw a dart and hit the same place every time, that’s precise, even if you miss the dart board entirely.

Types of metrology

There are three main fields of metrology. These are scientific metrology, industrial metrology, and legal metrology.

Scientific metrology focuses on research and development to maintain standards and improve measurement techniques. It takes place in highly specialised institutions and research laboratories. It supports scientific research and innovation by creating ever more precise and accurate measurements. This area of metrology is also responsible for developing the definitions of measurement units. Refining those definitions is a constant task as new research and innovations become available. In the hierarchy of calibration, Scientific metrology sits on the top tier. It establishes the primary standards.

Industrial metrology aims to ensure quality and consistency in manufacturing processes. It applies the standards and techniques developed in scientific metrology to commercial activities. It will involve calibrating and using measurement instruments to monitor production and ensuring products meet quality standards through quality control and quality assurance. Good industrial metrology practices form an integral part of process control and so improve operational efficiency, reduce waste and contribute to sustainability.

Legal metrology addresses things like trade, weights and measures, health and safety. It ensures measuring instruments used in commercial transactions are accurate and reliable, maintaining consumer confidence and fair business practices. Compliance with legal metrology standards is essential for businesses to avoid penalties and uphold their reputation.

Measurement techniques and tools

Metrology and measurement techniques employ many different tools and devices designed to ensure precision and accuracy across various industries.

There are common tools that most people would be familiar with like callipers and micrometers. In advanced settings, coordinate measuring machines (CMMs), laser scanners, laser trackers give high-precision measurements, enabling detailed analysis of complex geometries.

Recent advances in measurement technology have significantly enhanced tool capabilities. Innovations like optical measurement systems and 3D scanning technology have revolutionised the capture and analysis of measurements. These technologies provide real-time data, allowing users to make informed decisions quickly, improving productivity and quality control in manufacturing processes.

The role of software in metrology is also absolutely crucial. Modern measurement tools pair with advanced software solutions that process the data we collect and turn it into powerful insights. These platforms increasingly include AI for faster and easier operation, analysis and in the most recent advances, entire connected systems spanning whole production facilities.

Automated metrology

The traditional place for metrology and measurement equipment has been in environmentally controlled rooms, far away from the harsh conditions of the production floor.

This has benefits and drawbacks. Sensitive equipment loses accuracy when it’s exposed to noise and vibrations. A CMM exposed to changing temperatures is little more than a random number generator. Part inspection and verification can be a long process which creates bottlenecks. Metrology was seen as a check point or a safety net catching faulty products before they left the factory.

In recent years, metrology has entered a new era and it’s powering a fundamental change in the way we manufacture and produce products. Much research and innovation focuses on taking industrial metrology out of the inspection room and becoming an integrated part of production. This allows for faster response times and many more data points throughout the production process. When parts begin to deviate, automated processes can compensate in a fraction of a second.

World Metrology Day

Every year on 20May we remember the original agreement between the 17 founder nations of the Convention of the Metre, which took place in Paris 1875. It was an historic agreement and diplomatic treaty that set the foundations for the international standard of units.

Today there are over 50 signatories to the Convention of the Metre and that day has been officially recognised by UNESCO for creating an international commitment to a harmonised global system of measurement. It’s something we take seriously here on the Manufacturing Intelligence blog and over the years we’ve always contributed to the conversation. In 2025 the theme was measurement for all times and all people, and we took a look at how the history of metrology mirrors the history of humanity itself.

Additionally, in 2024 we investigated some of the ways that metrology is supporting sustainability projects and improving the way we manufacture things. Measurement undoubtably has an important role to play in sustainability. When you can measure something, you begin to understand that thing a bit better. You can quantify and understand how its changing which is vital as we search for ways to improve the world around us.

Hexagon and the world of metrology

Hexagon’s involvement in the world of metrology began with the acquisition of Brown and Sharp in 2001, but the documented history of metrology goes back as far as the ancient Egyptians.

Nowadays, Hexagon supplies the broadest portfolio of metrology hardware and software in the world. Our research and development teams claim that with Hexagon technology, you can measure anything, anywhere: from microns to Mars.

Looking towards the future, the science of measurement is sure to support and accelerate innovation. The future of metrology is likely to see an increasingly integrated approach with a focus on quality control and quality assurance. In the world of metrology, the journey from ancient tools to modern innovations reflects humanity’s desire for better, for improved quality.

As technology advances, Hexagon will remain at the heart of progress, ensuring accuracy, innovation, and quality for life.