Rules for Significant Figures Version Number 1 Rule #1: All non-zero digits are significant. Rule #2: Zeros in front of a number are not significant. Rule #3: Zeros between non-zero digits are significant. Rule #4: Zeros at the end of a number are significant if there is a decimal point in the number. Version Number 2 Use this diagram to help determine the number of significant figures in a measured value… Pacific Atlantic If the decimal point is present, start counting digits from the Pacific (left) side, starting with the first non-zero digit. 0.003100 (4 sig. figs.) If the decimal point is absent, start counting digits from the Atlantic (right) side, starting with the first non-zero digit. 31,400 ( 3 sig. figs.) TAKEN FROM: http://www.kentchemistry.com/links/Measurements/sigfigs.htm RULES FOR SIGNIFICANT FIGURES The Atlantic Pacific Rule (1) Pacific – "P" is for decimal point is present. If a decimal point is present, count significant digits starting with the first non-zero digit on the left. Examples: (a) 0.004703 has 4 significant digits. (b) 18.00 also has 4 significant digits. (2) Atlantic – "A" is for decimal point is absent. If there is no decimal point, start counting significant digits with the first non-zero digit on the right. Examples: (a) 140,000 has 2 significant digits. (b) 20060 has 4 significant digits. Imagine a map of the U.S.; If the decimal is absent count from the Atlantic side. If the decimal point is present, count from the Pacific side. In both cases, start counting with the first non-zero digit. Calculations shouldn't have more precision than the least precise measurement. This leads to 2 rules: (A) For addition and subtraction: The answer should not have more places past the decimal than the number with the least places past the decimal. Example: 1.2 + 12.348 = 13.5 Not 13.548 (B) For multiplication and division: The answer should not have more significant figures than the number with the least amount of significant figures. Example: * 502 x 3.6 = 1800 Not 1807.2 These last 2 rules can be called the Many-Places rule. For mult/div, how many significant figures is important. For plus/minus, number of places is important. TAKEN FROM: http://www.amityregion5.org/bburt/ESciResources/SIGNIFICANT%20FIGURES.htm