Rounding and truncation
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Rounding to the nearest ten, hundred or thousand
Rounding to a stated power of ten, keeping the zeros that hold the place values.
Rounding to decimal places
Rounding a decimal to a stated number of places from the next digit only.
Rounding negative numbers
Rounding along the number line, so −3.47 rounds to −3.5 and −3.44 to −3.4.
Rounding to significant figures
Finding the first significant figure and rounding from there.
Zeros and significant figures
Leading zeros never count, and zeros lost by rounding are written back.
Truncation
Cutting a number off at a decimal place or significant figure, not rounding.
When the context forces the direction
Rounding up regardless of the digits when the context demands it.