**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. (:

How to Read a Ruler

Written by Jialynn

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