Error intervals
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Why a measurement is never exact
Why a reading is only ever accurate to half the smallest division on the scale.
Error intervals from rounding
The interval a rounded value came from, half a unit either side.
Error intervals from significant figures
Finding the rounding unit from the last significant figure, then the interval.
Error intervals from truncation
Why a truncated value is its own lower bound, with an interval one unit wide.
Working back from an interval
Recovering the stated value and its accuracy from an error interval.
Bounds of discrete quantities
Greatest and least possible values when a quantity counts whole items.