Significant Figures (count + round)

Count sig figs in a number; round to a target N. Leading zeros not significant; trailing zeros after a decimal ARE.

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Formula and source

Sig-fig count: non-zero digits are always significant; zeros between non-zeros are significant; leading zeros are not; trailing zeros after a decimal point ARE significant. Trailing zeros in a bare integer are ambiguous and NOT counted here (use scientific notation for explicit precision). Rounding to N sig figs: scale by 10^(N - ceil(log10(|x|))), round, scale back.

Significant-figure conventions per NIST SP 811 ยง7 (Guide for the Use of the International System of Units).

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