SI Units

[Simon "M." Jerome <smj1@npl.co.uk>]

Hi.

I don't have an axe to grind, so here are a few observations.

Perhaps the underlying message here is that none of us like change. For 
example, having been raised on feet, pounds, pints &c, &c, I find it 
easy to visualise the world with those units. My children, however, are 
being bought up on metres, kilograms, litre &c, &c and find it easy to 
visualise the world in those terms. We are all more comfortable with 
the systems we are familiar with.

I work with radioactivity and find the Becquerel simple, 
straightforward and practical in that is a measure of the number of 
events happening per second and rather than being related to the mass 
of an amount of Radium with the same disintegration rate, as the Curie 
used to be.

The Curie used to be defined as noted above, and was a practical 
measure of radioactivity at the time; but it is no more or less 
practical than any other definition. The Curie is very useful for 
describing large amounts of radioactivity and impractical at the 
environmental level where the Becquerel is far more meaningful.

The main advantage of the SI and metric systems is that they are simple 
(based on multiples of 10) and thus should lead to fewer errors, ie;

10 millimetres = 1 centimetre
100 centimetres = 1 metre
1000 metres = 1 kilometre

12 inches = 1 foot
3 feet = 1 yard
1760 yards = 1 mile (and there are any number of chains, furlongs and 
so forth to contend with as well!)

However, the metric system is a little boring when it gets to 
terminology and the decimalisation of the UK currency illustrates this;

Pre 1971 we had;

Pennies (1d, derived from the Roman denarii, see also Marks and 
pfennigs)
Ha'pennies (½ d)
Tanner (6 d piece)
Bob (1 shilling/ 1s - 12d, see also the Austrian schilling)
Florin (2s, from the Florentines)
Half Crown (2s 6d, also known as half-a-dollar from the time when 4 US 
$ = £1)
Crown (5 s)
Pound (£1 = 20 s)
Guinea (21 s, from Africa, where the Gold was mined. Used for the 
payment of bribes and other transactions between gentlemen)

We now have pounds of 100 p (pron. pee).

Finally, don't forget that the Convention du Metre - signed up to in 
1875 by many countries, including the USA - was set up primarily for 
the purposes of trade, and not for the benefit of the scientific 
community.

Have a good weekend
Simon Jerome

simon.jerome@npl.co.uk
http://www.npl.co.uk

DISCLAIMER:

"The contents of the above message are my views alone and should not be 
taken as representing the views held by NPL management Ltd."