Introducing uncertainty
A measurement can never be exactly right, it will always be subject to a certain amount of uncertainty.
Uncertainty of measurement is the doubt that exists about the result of any measurement. You might think that well-made rulers should be trustworthy and give the right answers. But, for every measurement - even the most careful - there is always a margin of doubt. In everyday speech, this might be expressed as ‘give or take’ ... e.g. a stick might be two metres long ‘give or take a centimetre’.
Imagine measuring the height of Jeff with a ruler. The nearest centimetre will suffice. (Which is to say that the uncertainty of the reading is about half a centimetre. However if uncertainty of a millimetre was needed the measurement would be a lot trickier. Do you flatten his hair?
A good measurement may be meaningless without knowing the uncertainty.
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