Uncertain Digits
1. Only used when recording any measurements.
2. Each measured number has only ONE uncertain digit (the last digit written.)
3. Each measured number (with its ONE uncertain digit) reflects the accuracy of the
scale that was used in the measurement.
Example: If the recorded measurement = 3.476g, the accuracy of the scale is
to the nearest 0.01g (the hundredths place), and the uncertain digit is the 6 (the
thousandths place).
4. When adding or subtracting measured numbers, the answer should reflect the
LEAST accurate scale used in the measurements.
a. Example: 3.145
+ 2.1244
5.2694 (calculator answer)
5.269 final answer using the correct uncertain digit
Significant Figures
1. Only use when you are multiplying or dividing measured numbers (examples:
volume, density).
2. Significant Figure (sig. fig.) RULES:
a. Nonzero numbers are ALWAYS significant.
i. 396 has 3 sig. figs, 65432 has 5 sig. figs.
b. Zeros between nonzero digits are ALWAYS significant (“sandwiched
zeros”)
i. 7609 has 4 sig. figs, 5.0004 has 5 sig. figs.
c. Zeros that fall both at the end of the number AND after a decimal point
are ALWAYS significant.
i. 0.00020 has 2 sig. figs., 35.0 has 3 sig. figs.
d. Zeros that act as placeholders are NEVER significant.
i. 0.02 has 1 sig. fig., 0.0026 has 2 sig. figs., 400 has 1 sig. fig., 400.
has 3 sig. figs
3. In multiplication or division, the resulting answer must be reported with the same
number of significant figures as the measurement with the FEWEST significant
figures.
392.3m x 2.45m = ________________calculator answer
_________________ final answer
Decimals and Rounding Decimals: See # 378-379 in your Sciencesaurus Handbook.
Metric Units: See #55-72 in your Sciencesaurus Handbook. Remember: NO NAKED
NUMBERS! Measurements without a unit are meaningless in science. All of your
measurements must have a unit label!