Significant figures
The meaningful digits in a measurement or calculated result, reflecting the precision of the measurement or appropriate rounding. The number of significant figures should match the least precise measurement in a calculation. Rules include: non-zero digits are always significant, zeros between non-zero digits are significant, and leading zeros are not significant.
Real World
CERN physicists reporting the Higgs boson mass as 125.35 GeV rather than 125 GeV communicate that their detector can resolve differences of 0.01 GeV — each extra significant figure reflects billions of pounds of engineering precision.
Exam Focus
Match your answer's significant figures to the least precise value given in the question — examiners penalise unjustified extra digits.
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