The powers that be of the metric system are wrestling with the problem of defining the kilogram independently of an actual physical object (i.e. the very slowly degrading cylinder of platinum-iridium alloy kept at Sèvres, near Paris, known as “the international prototype of the kilogram”). Meanwhile, they are neglecting a longstanding question that urgently cries out for a solution. [Article contributed by Martin Clutterbuck].
At the 99th meeting of the Comité International des Poids et Mesures (CIPM) in October 2010, a draft specification for changes to the definitions of units was recommended to be submitted to the General Conference on Weights and Measures (CGPM) at its 24th meeting to be held in October 2011.
The SI brochure, which will contain all the revisions and is currently in its 8th edition, is managed by the Bureau International des Poids et Mesures (BIPM). The BIPM is supervised by the CIPM which is in turn is supervised by the CGPM!!
The draft states that the meeting will have considered “the international consensus on the importance, value, and potential benefits of a redefinition of a number of units of the International System of Units (SI)”*.
“the kilogram will continue to be the unit of mass, but its magnitude will be set by fixing the numerical value of the Planck constant to be equal to exactly 6.626 06X ×10-34 when it is expressed in the SI unit m2 kg s-1, which is equal to J s” **
[The symbol X represents one or more additional digits to be added at the time that revised definitions of the SI Brochure are finally adopted.]”
Well, yes, precisely, but is the average market trader or any other trader for that matter, going to rush to take any old imperial scales to the dump as a result? More likely, any down-to-earth Brit will say that all this proves is that metric is all about science – astrophysics and all that stuff so it doesn’t affect me!
Unfortunately, the CIPM and the BIPM can’t get their act together for one little thing that might just influence our old friend the ‘man-in-the-street’, the market trader or even ‘red-top’ newspaper journalists.
And what might that be? Well it’s another old friend, the symbol for the litre.
Surely the SI should not continue to offer the option of the use of either the lowercase ‘l’ or the uppercase ‘L’. Indeed the confusion caused and the understandable desire of catalogue and product labelling graphics artists to be as clear as possible has led to many examples of the use of ‘Ltr’ instead of either of the correct symbols.
Some products even mix uppercase ‘L’ with lowercase ‘l’ on the same label!
The CIPM, in 1990, considered that it was still “too early” to choose a single symbol for the litre… but how long do we have to wait for a decision?