Product Regulation and Metrology Bill [Lords]

Debate between John Hayes and Adam Thompson

2nd reading
Tuesday 1st April 2025 Commons Chamber

[Adam Thompson]

Certainly. It is not a new word as far as I am concerned; I believe it was brought into common parlance in the Victorian era.

I will move on to some more examples. There is the James Webb space telescope—something more modern than the pyramids. It takes images of our universe more than 13 billion light years away that are deeper, more brilliant and more beautiful than anything we have ever seen. Behind that, there is the construction of a 6.5-metre mirror, flat to within just a few tenths of billionths of a metre from its highest top to its smallest valley. If we were to expand the size of the 6.5-metre mirror to the size of the Earth, the distance from the highest mountain to the deepest valley would be of the order of the height of my hip.

Behind the discovery of gravitational waves, there is a series of interferometers, kilometres in size, which can detect signals from noise at levels considered unachievable throughout human history until the past 20 years or so and which are capable of listening to the collision of black holes across spacetime.

[Sir John Hayes]

I hesitate to interrupt the hon. Gentleman, because he is making a wonderful contribution to our affairs, which is indicative of the beauty of science, about which we hear too little. Before he rushes—hurtles, one might say—into the future, can he say a word about the peculiarly British measurements that informed my childhood? I mean things such as pecks, perches, rods and bushels, for each of those was rooted in the way that he described.

[Adam Thompson]

I am grateful to the right hon. Gentleman for his intervention, and I am happy to explain. Those particular forms of measurement are not in common use any more, but of course many right hon. and hon. Members of this House will have grown up with them. Broadly, the ones that are still in use are defined in the modern parlance, but it is important to remember that the modern metric system accounts for all of those heritage measurements. The common inch, for example, is formally defined as 25.4 mm, and while I apologise to Members across the House, it is important for me to let them know that the pint is formally defined as 568 ml. Those heritage measurements and, indeed, the entire imperial system are now referenced on to the metric system; defined very simply, the imperial system is the metric system. There is no reason why we should not use those historical measurements—where they are useful, they are perfectly valid—but they are formally defined with reference to the modern metric system. I will talk more about this shortly.

Metrology lies at the heart of everything we know, from telescopes to speed cameras and from knee replacements to jet engines. Every single thing made by human hand was designed first, constructed second and then checked by a metrologist to ensure it met its specifications—if we cannot know it, we cannot improve it. However, ensuring that parts meet their specifications is not simple, as each measurement, dimensional or otherwise, has an associated measurement uncertainty. That is a non-negative parameter characterising the dispersion of the quantity values being attributed to the thing being measured, based on the information used. Estimation of measurement uncertainty is a complex procedure—one that formed much of my career prior to coming to this place—and is usually performed in line with the “Guide to the expression of uncertainty in measurement”.

Uncertainty estimation is generally performed by making measurements that are traceable to the definition of the SI metre—when we are concerned with the metre. Again, the “Vocabulaire international de métrologie” defines traceability as a property of a measurement result whereby the result can be related to a reference through a documented, unbroken chain of calibrations, each contributing to the overall measurement uncertainty. Traceable measurements allow for the successful estimation of uncertainty and are generally a base requirement for the verification of manufactured goods. Traceability is considered by the international community to be the only means by which evidence can be provided towards a given product fulfilling the requirements set out by its designer.

To provide an example, let us consider a length measurement made between two faces of a manufactured part, such as a Rubik’s cube. Imagine that I am holding a Rubik’s cube—I could not possibly have brought a prop, Madam Deputy Speaker. The length between two faces could be measured by a calliper. That calliper would be calibrated using a measurement artifact, most commonly a metal cuboid called a gauge block. That gauge block would in turn be calibrated by a more accurate instrument, which itself is calibrated using a more accurate gauge block. That more accurate gauge block would then be calibrated with reference to an optical interferometer using a laser source. That laser source is finally calibrated against the iodine-stabilised laser that is used to realise the definition of the metre, so traceability is established from the shop floor measurement all the way up to the definition of the metre by an unbroken chain of calibrations.