A significant figure (or significant digit) is any digit in a number that contributes to its precision and accuracy, reflecting the reliability of a measurement or calculation. These digits include all certain digits plus one estimated digit, representing the precision of the measuring instrument used. Key points about significant figures:

• All nonzero digits are significant. For example, 211.8 has four significant figures

• Zeros between nonzero digits are significant. For example, 20,007 has five significant figures

• Leading zeros (zeros to the left of the first nonzero digit) are not significant; they only indicate the decimal position. For example, 0.0085 has two significant figures

• Trailing zeros in a number with a decimal point are significant. For example, 12.000 has five significant figures, and 1.050 has four

• Trailing zeros in a whole number without a decimal point are generally not significant unless specified by scientific notation. For example, 500 has one significant figure, but 500. has three

Significant figures are essential in scientific measurements because they indicate the precision of the measurement, reflecting the smallest unit that the measuring instrument can reliably detect. When reporting or calculating values, significant figures help avoid false precision by limiting the digits to those that are meaningful and justified by the measurement

. In summary, significant figures are the digits in a number that carry meaningful information about its precision, including all certain digits plus one uncertain or estimated digit.