A new definition of the kilogram?

A new method of defining the kilogram is being sought by various teams of scientists around the world. However, it may be some years before a decision emerges. (NB – this will obviously not alter the actual size of the kilogram). This article, contributed by Martin Vlietstra, will be of interest to the more technically minded.

The kilogram is an anomaly in the world of physical constants – its current definition relies on a particular artefact or object – the prototype kilogram that is held by the BIPM on behalf of its “shareholders”, its subscriber governments. Every other physical constant is defined in terms of one or other physical phenomena that can, in principle, be measured in any laboratory in the world. Ever since the retirement of the prototype metre in 1960, scientists have been looking for a means of defining the kilogram by means of a scientific experiment and yet maintaining the accuracy that can be obtained using the prototype kilogram

One of the projects to redefine the kilogram is to define it in terms of a sphere of silicon. Such spheres are currently being produced in the laboratories of the Australian Council for Scientific and Industrial Research (ACSIR) – See http://www.theage.com.au/news/national/making-an-exact-difference/2007/06/14/1181414466901.html.

Once the sphere has been manufactured, there are a number of problems associated with defining the kilogram. Firstly, the diameter of the sphere must known to an accuracy of better that one part in 10^8. If the sphere has a mass of exactly one kilogram, its radius will be approximately 93.58 mm, so its diameter needs to be known to better than 1 nm (which is approximately two wavelengths of light). Details of some of the scientific techniques used and the participating laboratories (Australian, Belgian, British and German [in alphabetic order]) can be found at http://www.npl.co.uk/mass/avogadro.html.

In addition to measuring the diameter, the scientists concerned will need to identify which is the more practical – to define the kilogram in terms a specific number of silicon atoms or to define it in terms of the mass of a sphere of specified radius. Part of the experiments currently under way is to decide which of the two techniques give the better results.

This is not the only experiment that is being developed to redefine the kilogram; another is the Watt Balance which is being carried out by the BIPM. (See http://www.bipm.org/en/scientific/elec/watt_balance/ ).

Who will decide which experiment is the better? This will ultimately be decided by the CGPM on the advice of the CIPM and is likely to be some years off.

CGPM = Conférence Générale des Poids et Mesures / General Conference on Weights and Measures, a body consisting of representative of the governments that have subscribed to the Convention of the Metre.

CIPM = Comité International des Poids et Mesures /International Committee of Weights and Measures, a body of 18 eminent scientists elected by the CGPM.

Will the new metric clothing standard work?

A new international standard for sizing clothes would overcome many of the problems of incompatible size labelling. But will it be undermined by the British retail and clothing industries because it is metric? – article based on contribution by M-V.

During the last few days there have been various newspaper articles describing proposed new labelling for clothing. This labelling is in fact the EN 13402 European standard for labelling clothing sizes and is expected to come into widespread use by the end of 2007. The work was sponsored by CEN (European Standards Organisation – an organisation that draws its membership from various European bodies), while much of the fieldwork was done by the BSI (British Standards Institute). The photograph below (by Markus Kuhn and downloaded from the Wikipedia site) shows an actual label used for a high-visibility jacket.

This example shows that the garment is designed to fit a man with a chest measurement of 118 to 124 cm and a height of up to 1.94 m.

The standard works as follows.
(Wikipedia http://en.wikipedia.org/wiki/EN_13402
has a full description – also written by Markus Kuhn). Firstly, it should be remembered that measurements on the garments refers to the wearer, not to the garment itself. Thus the chest measurement on a vest label and on an overcoat label for a particular person have the same value.

The standard comes in four parts:

  • EN 13402-1 defines how the body should be measured (using centimetres and kilograms where appropriate). For example, the length of the hand girth is measured “maximum girth measured over the knuckles (metacarpals) of the open right hand, fingers together and thumb excluded”. This results in a pictogram (diagrammatic picture) of the individual customer – as illustrated below:

Ideally, everybody should have a little card bearing this pictogram, and they can use this whenever they go shopping for clothes (or borrow their partner’s if they are shopping for them!) Enterprising clothing retailers might offer a free measurement and card-issuing service.

  • EN 13402-2 defines the primary and optional secondary measurements for various garments. For example, the primary measurement for men’s trousers is the waist girth, while the wearer’s height and inside leg length are optional additional measurements. The author has spotted one omission is the list of garments â?? there is nothing about men’s kilts, though manufacturers might use the same parameters as are used for women’s skirts.
  • EN 13402-3 defines the standard interval sizes for various measurements. For example men’s chest sizes will be in 4 cm intervals and a 100 cm chest would be suitable for men with chests between 98 cm and 102 cm.
  • EN 13402-4 defines a five character manufactures coding system.

If UK retailers adopt the system (it is optional), then there will be a big change – conversion of the sizes of existing clothing lines will be difficult because the traditional British interval for men’s chests (for example) is 2 in, not 4 cm. This will mean that manufacturers will have to offer the public a wider range of measurements to accommodate the smaller interval. Unless there is some coordination, one can see chaos on the high street if one retailer or manufacturer uses the EN 13402 while another sticks to traditional sizing.

“Units” of alcohol

How should the alcohol content of drinks be measured? – asks M-V

The unit of alcohol is defined as 10 ml of pure alcohol and is unique to the UK (and possibly Eire). Other EU countries have developed their own “units of alcohol”, and Wikipedia lists seven or eight different units for different countries.

Should there be a standard “unit of alcohol” (defined as one centilitre which is the UK definition) or should each country continue to define its own unit of alcohol. If so, who should take the lead in making this definition – the EU, WHO, UN?

Are UK height, width and weight restrictions enforceable?

A contributor asks whether the failure of UK signs to use the correct international symbols could enable lawyers to get their clients off fines for motoring offences.

One of the guiding principles of the SI Brochure [the manual of the BIPM – International Bureau of Weights and Measures, who regulate the metric system) is that each unit of measure should have its own unique symbol. All units of measure that are included have been allocated symbols. These symbols include:

  • T (upper case) – teslas (strength of a magnetic field)
  • t (lower case) – tonnes
  • ‘ (single apostrophe) – minutes of arc
  • ” (double apostrophe) – seconds of arc

(No symbol was allocated for “mile”, which should be written in full.)The SI manual formed the basis of the EU directive on metrication. When the British Government negotiated with the governments of our partners in the EU to retain the foot and inch, one of the clauses of the agreement extended the catalogue of units to include feet and inches for use in certain circumstances and subject to specified conditions. When they were incorporated into the catalogue, they were allocated the following symbols:

  • ft – Feet
  • in – inches

What has the UK Government done?
On height and width restriction signs, one sees feet and inches denoted by single and double apostrophes respectively, while on weight restriction signs, one sees “T” (upper case) used to denote tonnes on weight restriction signs (OK, the law permits a lower case “t”, but I have yet to actually see one on a road sign in Britain – the law in question is – Statutory Instrument 2002 No. 3113 – The Traffic Signs Regulations and General Directions 2002 – the “TSRGD”).

The TSRGD also allows the use of the symbol “m” sometimes to denote “mile” and sometimes “metre”.

To the best of my knowledge, this has yet to be tested in a United Kingdom court – if it were, would the court rule that these signs are unenforceable due to the technicality of the incorrect use of symbols? One must remember of course that under the European Communities Act 1972, the courts would be obliged to pass judgement “in accordance with the principles laid down by and any relevant decision of the European Court”.

If such a case heard in a UK court and the road signs declared unenforceable, the first people to be affected would be those people who live on a “rat-run” where heavy vehicles are prohibited by width and weight restriction signs. The councils representing such people can take preventative action against the these signs being declared unenforceable by ensuring that weight restriction signs use the lower case “t” to denote “tonnes” and that width restriction signs clearly display both metric and imperial units.

[Please note:
Neither the author nor UKMA are able to offer any formal legal advice. The views published above are the views of the author who has not had formal legal training. The UKMA do not necessarily endorse these views. If somebody wishes to pursue a matter based on these views through the courts, they should seek proper legal advice from their solicitor.]

[article submitted by MV]

Metric howlers – Times hat-trick

When converting metric units into imperial units, journalists (or more likely sub-editors) are apt to make mistakes, especially if they are dealing with subjects with which they are not very familiar. On the 9th December 2006, The Times managed a hat-trick of blunders. [article contributed by MV]

Page 8 – Airlines should pay full cost of their pollution

The penultimate paragraph contained the text “[Boeing and Airbus] Aircraft use an average of four litres of fuel per 100 km”. This sentence should have raised the alarm bells – a consumption of 4 L/100 km is what one would expect of an economical car such as the Smart Car. (The imperial equivalent is 70 mpg!). If the writer used metric units when driving they would have spotted this howler.

Page 43 – Why the Dead Sea is dying

The fifth paragraph contains the phrase “to suck 1,900 million cubic metres (2.1 million cubic yards) of water”. This phrase contains two howlers. Firstly, a factor of 1000 seems to have gone missing. Secondly, the writer appears to have used a factor of 1.1 to convert cubic metres to cubic yards when the correct factor is 1.1 x 1.1 x 1.1 (which is equal to 1.331).

Page 44 – Spend a penny, but it make you think of a tenor

The third paragraph contains the sentence “The block, in Calcutta, is spread over 3,000 square metres (3,300 square yards) and is “. Here, the writer used a factor of 1.1 to convert square metres to square yards. The correct factor is 1.1 x 1.1 (which is equal to 1.21).