Accuracy/Precision and Measurement/Uncertainty

Accuracy and Precision

The textbook definitions (which are always useful) for accuracy and precision are:

-Precision is how reproducible a measurement is compared to other similar measurements. So how hard or easy is it to reproduce that measurement?

-Accuracy is how close the measurement (or average measurement) comes to the accepted or real value.

A good example of this would be a game we played in elementary school. We would play frisbee-golf where you have to throw the frisbee into the hulahoop (like a golf hole) and play the entire playground exactly like it is a golf course. So if you think about the hulahoop being the accepted or real value, accuracy is how close you can come to it when throwing the frisbee.


Measurement and Uncertainty

Every measure you will take or see is only an estimate, which has some degree of uncertainty.

Absolute uncertainty:

The uncertainty expressed in the units of measurement. There are 2 methods of doing this. Make sure to try both!

Method 1: Make at least 3 measurements. Calculate the difference between the average and the lowest or highest reasonable measurement. Be sure to include a +- sign at the beginning of the answer (I don't have that symbol on my computer)

Method 2: When making a measurement, always measure to the best precision you can (remember, precision is reproducibility!) Therefore, you should estimate to a fraction 0.1 of the smallest segment on the instrument scale.

Now, time for exactions! Here is how to calculate relative uncertainty:

Relative Uncertainty = absolute uncertainty / estimated measurement

Relative Uncertainty can be expressed in percentages or using significant figures.

Here is a video for your viewing pleasure, the guy really seems to know his chemistry stuff!

Super Cool Video