SI is now in use (almost) everywhere in the world but some businesses, some sectors have their own units. The physician has just measured your blood pressure: he tells you "13 - 8", that is all right. However if you dare to look at his device you read 130 - 80: effectively your blood pressure, displayed in millimeters of mercury. You could have expected "173 - 106" (hectopascals). However the measurement of pressure of blood and other human body fluids benefits from a quite official derogation from European directive 85/1/EEC, stemming itself from a World Health Organization recommendation, extending the use of millimeters of mercury - not centimeters. Quite often in our day to day life we face such deviations from the purity of SI. Nothing serious when our blood pressure is at stake, since physicians legally use a metric unit, albeit obsolete. However in many other sectors Anglo Saxon units, even ancient units, are common; we are so much used to them that we don't even notice them.

Computers It is a common belief that the computer industry, dominated by the United States, uses American units. Not totally true. Remember the time where the 3 1/2 inches floppy disk was the ubiquitous storage medium, and check its size with calipers: you will find exactly 90 mm (indeed 90 by 94 mm). CDs and DVD diameter has always been 120 mm. Even the mini-CDs, often called 3-inches disks, are 80 mm in diameter. As far as hardware is concerned the situation is even more confusing: motherboards and connectors of first generations desktop PCs use American units; as an example, the spacing between connector pins used to be 1/5 inch (5.8 mm); for more recent connectors spacing is 5.00 mm. This may explain why some connectors are not easy to plug inŠ Extension cards (PCI) for desktop computers are designed according American standards, e.g. 12 inches; those for laptop computers (PCMCIA) have always been metric, even if the 50 mm card is normally named "2 inches". The same mix of units is found with monitors: the screen (diagonal) size is specified in inches, e.g. 17", but the resolution (dot pitch) is always given in millimeters, e.g. 0.25 mm.

Car power Soon governments realized that automobile could be a profitable source of taxes. As soon as cars became popular, it appeared necessary to modulate the basis of taxation: power seemed to be the most equitable basis. But, in the early years of the car industry, measuring power of internal combustion engines was not easy. Formulas, often based on displacement, were therefore developed to estimate power. For instance, in Great-Britain, power was simply defined as hp = 0.1 L, L being displacement (please notice the use of metric and decimal, yes, in the UK!). Thereafter formulas were made more accurate in taking into account cylinder diameter, compression rate, etc. Most countries have long ago abandoned such a concept of "administrative" or "fiscal" power, but not France: here the formula, certainly developed by engineers from "Ecole Polytechnique", had reached a high level of sophistication: type of fuel, total displacement, gearbox ratios, were elements of the formula. At that time the administrative power was also used to determine the insurance premiums; more often than not it thus occurred that the base version of a certain car had to pay a higher premium than the sport version of the same model, more powerful, more expensive, and much more dangerous! Since 1988 the formula is somewhat more logical, as well as more ecological: the fiscal power is just a function of power (now in kilowatts!) and of carbon dioxide emissions. In passing, since the ignominious "vignette" [tax label] has been canceled, it is only used to establish the registration tax.

Sea transport Since a long time depth is measured in meters and no longer in fathoms (of six feet, i.e.2 yards or 1.83 m). Also gone away the time where the sailor at stem of Mississippi ships shouted "mark twain" (the second mark) when depth below two fathoms threatened the ship safety: the word pleased so much to Samuel Langhorne Clemens that he took it as nom de plume. Equally it has been forgotten that at the beginning of the nineteenth century the US territorial waters were a cannon range wide, around three miles. Everything else is metric, with the exception of length of leisure boats, whether sail or motor: even for those made in Europe, hull length is given in feet. Certainly a mark of snobbery - actually some old fishermen in Brittany also give the length of their boats in feet... The younger ones may well no longer know what a nautical mile is; thanks to their GPS (Global Positioning System) they see their position on metric maps with an accuracy of a few meters.

Air transport Therefore risks are obvious: if pounds or kilograms are confused, the aircraft will crash at the end of the strip because too loaded to take off, or conversely will run short of fuel during cruse. And this happened, at least one time: on 23 July 1983 the Boeing 767 of Air Canada flight 143 from Montreal to Edmonton was quietly cruising above the Manitoba prairie at an altitude of around 13 000 meters when both engines went dead: tanks empty. The pilot had a long experience in gliding: at the end of a 15-minute glide he succeeded in landing the aircraft without much damage on a military landing strip no longer in use - except for go-kart amateurs, just timely evacuated by the Canadian mounted police, efficient as usual. No casualties, just a strong fright. Later the enquiry established that the pilot effectively had ordered the 22 600 kg of kerosene needed for the flight but that the ground staff had loaded 22 600 pounds.

The oil barrel... Its origin is obscure. It is said that in 1866 some oil producers of Virginia were granting a discount to customers purchasing their lamp-oil directly from the drill by adding 2 extra gallons to any order of 40 gallons. Also that in Ohio, the leading oil production site in the middle of the 19th century, oil was transported in 50 gallons wood barrels on horse-driven wagons; because of leakage and evaporation there remained only 42 gallons in the barrels at the end of the trip.

and cloth sizes. At least for shoes is there a beginning of standardization. Not yet for clothes. Imagine (dream about...) a lady of a "model" size; in the USA she would order size 12 or 14; the same in New-Zealand, Ireland, and Great Britain - but there the mark could be 8 or 38; she would need 32 in Canada, 34 in the Netherlands, 38 in Iran, 40 in Germany, Denmark, Israel, Switzerland and Yugoslavia; but C 40 in Sweden and NC 40 in Finland; 81 in Bulgaria; 92/99 in Japan; and 164/80/94 in Hungary... Now, is that really serious?

metrication

genesis

building

time

Treaty of Metre

United Kingdom

United States

conclusion