In my house I have four , I sometimes adjust them so that at least two, but rarely more than three, strike the hour within a few seconds of each othe… - Terence Quinn

... of may allow us to say that "this object is hotter or colder than that one." But even this apparently simple statement is fraught with pitfalls for the unwary. For example, take hold in turn of a block of , a piece of expanded and a rod of , all near room temperature but differing slightly slightly in temperature from one another. It is not easy to make any useful statements about which is hotter or colder. This means, of course, that the is a poor thermometer, but the reasons for this being so are by no means straight-forward: they are related to the way in which sensations of hotness and coldness are generated in the human body ...

On 19 March 1791 five of the great luminaries of French science, Laplace, Lagrange, Condorcet, and , met at the in Paris and drew up a document that laid down the definition of the new basic unit of length, the , for the proposed new system of measurement that would become the .

, the science of measurement, is part of the essential but largely hidden infrastructure of the modern world. We need it for high-technology manufacturing, human health and safety, the protection of the environment, global climate studies and the basic science that underpins all these. Highly accurate measurements are not exclusively the preserve of the and engineering; many areas of chemistry, and medicine are now dependent on accurate quantitative measurements. in all manufactured and agricultural products is strictly controlled by regulations that need accurate metrology for their implementation.