Thursday, October 28, 2010

Accuracy and Precision

Accuracy-->how reproducible a measurement is compared to other similar measurements
-->can be described as the correctness of a measurement

Precision-->how close the measurement (or average measurement) comes to the accepted or real value
-->can be described as the exactness of a measurement

*no measurement is exact
-every measurement is only one's best estimate, as it has some degree of uncertainty
-measurements are only exact when they are counted
eg. a family of 4

Absolute Uncertainty

-Uncertainty is expressed in the unit of measurement, not as a ratio or fraction
-there are 2 methods:
Method 1:
1. Make at least 3 measurements
2. Calculate the average between the measurements
3.Calculate the different between the average and the lowest or highest reasonal measurement. The largest difference will be the absolute uncertainty.

Method 2:
1. Make the best precise measurement, estimate to a fraction 0.1 if the smallest segment on the instrument scale.

Relative Uncertainty and Sig. Figs.

Relative Uncertainty=Absolute uncertainty/estimated measurement
-relative uncertainty can be expressed as a percent, or with sig. figs.

Practice reading scales, and identifying the uncertainty of each measurement using method 2.

Watch this video! It'll help. (: