Measurement uncertainty — Chemistry, 14–17
Every measurement has a limit to its precision. You learn to report results honestly instead of pretending that an instrument gives more certainty than it can.
What uncertainty means
A measured value is never perfectly exact: the scale, the method and your reading all have limits. If a balance shows 2.35 g to the nearest 0.01 g, the true mass lies very close to that value, not at a magically exact point.
Why report a range?
Scientists need to compare results and decide whether a difference is meaningful. A range such as 10.0 ± 0.1 cm says what the instrument can support; writing 10.000 cm would claim information nobody measured.
Combining uncertainties
You measure a length as 12.0 ± 0.1 cm and another as 8.0 ± 0.1 cm. For the total, add the central values: 20.0 cm, and add the absolute uncertainties: 0.2 cm. Report 20.0 ± 0.2 cm.
The trap: more digits means better
It feels scientific to write many decimal places, especially when a calculator displays them. But a calculator only processes your input; it cannot create precision that the measuring instrument never supplied.
Where it is used
In a laboratory, uncertainty helps you judge whether two methods give genuinely different results. Engineers use it when testing materials, and pharmacists use it when deciding whether a measured dose is safely within its target.
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