Measurements have uncertainty — Data, 11–13 years
A measurement is an estimate made with a tool, not a perfect window onto reality. Its scale, the object and the person measuring all limit how exact the result can be.
A measurement is an estimate
When you measure length, time or temperature, the result depends on the tool and how you read it. A ruler marked in millimetres can tell more than one marked only in centimetres, but neither gives endless digits. The sensible result includes the level of detail the tool can support.
Why record the limits?
The problem is that two careful people can measure the same object and get slightly different answers. This happens because readings are rounded and tools are never perfectly fine. Recording the likely uncertainty stops a small difference being mistaken for an important one.
Measuring a pencil
A ruler with millimetre marks shows a pencil ending between 12.3 cm and 12.4 cm. You estimate 12.35 cm, or round to 12.4 cm if the task needs one decimal place. You should not write 12.350000 cm, because the ruler did not measure that much detail.
More digits do not mean more truth
It is tempting to copy many decimal places from a calculator and call the answer precise. But a calculator can only process the information you entered; it cannot add detail that the measuring tool never captured. Extra digits may make a guess look more certain than it is.
Building, cooking and weather
A builder allows for measurement limits when cutting wood, and a cook chooses a suitable scale for flour or liquid. Weather reports also round temperatures because a forecast of 18.347 °C suggests more certainty than the instruments and changing air can provide. Good data is honest about its precision.
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