Absolute |
Relative |
Absolute values have the same units as the quantities measured. For example, 0.2314 grams, or plus or minus 0.02 mL. |
Relative values are ratios, and have no units. The ratios are commonly expressed as fractions (e.g. 0.562), as percent (fraction x 100, e.g. 56.2%), as parts per thousand (fraction x 1000, e.g. 562 ppt), or as parts per million (fraction x 10^{6} , e.g. 562,000 ppm). |
Absolute Accuracy Error Example: 25.13 mL - 25.00 mL = +0.13 mL absolute error |
Relative Accuracy Error Example: (( 25.13 mL - 25.00 mL)/25.00 mL) x 100% = 0.52% relative error. Example: For professional gravimetric chloride results we must have less than 0.2% relative error. |
Absolute Precision Error standard deviation of a set of measurements: standard deviation of a value read from a working curve Example: The standard deviation of 53.15 %Cl, 53.56 %Cl, and 53.11 %Cl is 0.249 %Cl absolute uncertainty. |
Relative Precision Error Relative Standard Deviation (RSD) Coefficient of Variation (CV) Example: The CV of 53.15 %Cl, 53.56 %Cl, and 53.11 %Cl is (0.249 %Cl/53.27 %Cl)x100% = 0.47% relative uncertainty. |
David L. Zellmer
Chem 102
February 9, 1999