How long is a piece of string

A common problem in Anglo Saxon England, as well as much of contemporary Europe, was the way cloth merchants could so easily cheat the common people. At a market, it was all too easy to ask for a yard of cloth, to see it measured against the merchant s yardstick, and pay for the cloth only to get home to learn just how short the merchant s stick was. Paying for 10 yards and coming home with only 9 yards was common, it seems and the problem was not restricted to just cloth, but also to leather and timber. 

While feet and yards are still used in Britain and other countries, the usual length is now the metre. At the time of the French Revolution in the 18th century and soon after, the French Academy of Sciences sought to systemize the measurement of all scientific quantities. This work led eventually to the concept of the Systeme Internationale, or SI for short. Within this system, all units and definitions are self-consistent. The SI unit of length is the metre. 

The original metre rule was kept in the International Bureau of Weights and Measures in Sevres, near Paris, and was a rod of 

SI units are self-consistent, with all units being defined in terms a basis of seven fundamental units. The SI unit of length / is the metre (m). 

This definition of more energy means hotter needs to be handled with care consider two identical weights at the same temperature. The higher weight has a greater potential energy. 

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In many respects, the above question is like asking How long is a piece of string - the answer will depend upon the precise circumstances and who is asked. It is probably true that most workers actively involved in this field have their own private definition. The rapid development of this area over the past decade or so is due to the endeavours of Jean-Marie Lehn more than any other, and it seems appropriate to commence with his own definition. 

Rare event Defining a rare event in flow cytometry is a bit like answering the question How long is a piece of string Particles that are less than 0.1% of the total are considered somewhat rare and require some care for enumeration in a flow cytometer. Really rare particles are less than 0.001% of the total and can be detected, counted, and sorted with careful gating based on multiparameters. 

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