Non-zero digits: All non-zero digits are significant.
Leading zeros: Zeros before the first non-zero digit are not significant.
Example: 0.0025 has two significant figures (2 and 5).
Captive zeros: Zeros between non-zero digits are significant.
Example: 105 has three significant figures (1, 0, and 5).
Trailing zeros: Zeros to the right of a decimal point and after a non-zero digit are significant.
Example: 3.00 has three significant figures (3, 0, and 0).
Trailing zeros in whole numbers: Are significant only if there is a decimal point.
Example: 1500 has two significant figures, but 1500. has four significant figures.