How can we determine the number of significant figures in measurements?

Rule 1: All nonzero digits in measurement are significant.

Rule 2: Zeros that appear between other nonzero digits (i.e., "middle zeros") are always significant.

Rule 3: Zeros that appear in front of all of the nonzero digits are called leading zeros. Leading zeros are never significant.

Rule 4: Zeros that appear after all nonzero digits are called trailing zeros. A number with trailing zeros that lacks a decimal point may or may not be significant.

Rule 5: Trailing zeros in a number with a decimal point are significant. This is true whether the zeros occur before or after the decimal point.