All non-zero digits are significant.
e.g. 27.4 mm has 3 sig figs.

Zeroes between non-zero digits are significant.
e.g. 2008 m has 4 sig figs.

Zeroes to the left of the first non-zero digit are never significant.
e.g. 0.0056 L has 2 sig figs.

Zeroes at the end of a decimal are significant.
e.g. 2.500 A has 4 sig figs.

For measurements written in scientific notation, the mantissa indicates the number of significant
digits.
e.g. 1.5040 x 10^{8} km has 5 sig figs.

Measurements with trailing zeroes but no decimal part are unclear.
e.g. We cannot tell if a measurement reported as 200 m was measured to the nearest hundred metres (1 sig
fig), the nearest ten metres (2 sig figs) or the nearest metre (3 sig figs). Such measurements must be
written in scientific notation to make sig figs clear.