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As we celebrate the 50th anniversary of the International System of Units (SI), NPL's Jonathan Williams explains just how essential the system is to science and society alike.

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Find out more about the SI

Listen to a short podcast of NPL's Peter Whibberley talking about the SI unit the second.

Download NPL's 'Units of measurement' poster

Read more

• Beginner's Guide to Measurement 
• SI Units poster
• Expressing Measurement Results
• SI Base Units 
• BIPM (2006), The International System of Units (SI), Eighth Edition, (Paris: Organisation Intergouvernementale de la Convention du Mètre)
• Fenna, D. (2009), Oxford Dictionary of Weights, Measures and Units (Oxford: Oxford University Press)
• Jerrard, H. G. & McNeill, D. B. (1992), A Dictionary of Scientific Units: including dimensionless numbers and scales (New York: Chapman and Hall)