French may be regarded by many as the language of love, but few may realise it can also be considered the language of science. Le Système International d’Unités, or the International System of Units (SI), was established in 1960 by the 11th General Conference on Weights and Measures (CGPM, Conférence Générale des Poids et Mesures). The CGPM, created by a diplomatic treaty called the Metre Convention signed in Paris in 1875, ensures wide dissemination and modification of the SI as necessary to reflect the latest advances in science and technology. The SI units consists of units of measurement devised around a number of base units (Table 1) While the physical and life sciences fully embrace this system, other related professions have been slower to fully appreciate it. Even in the clinical setting, using incorrect units to describe quantities is rife: how many of you have equipment, programs, or forms, which require you to enter weight in kilograms or height in centimetres? Using the SI units system, weight is reported in Newton’s (N) based on the formula: force (weight) = mass x acceleration (F=ma), while mass (kg) refers to the amount of matter contained in an object or being. An ‘out of this world’ example clearly illustrates the fundamental difference: a person with a mass of 80kg would weigh ~785N (F=ma [80kg x 9.81m.s-2]) on earth. If this person were on Mars, for example, their mass would remain the same but their weight would now be ~296N (80kg x 3.7-2).

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