Accuracy and Precision

Today, we have learnt the accuracy and precision of practises of measuring.
The following is the textbook definition:
Precision
It is how reproducible a measurement is compare to other similar measurements.

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

Measurement and Uncertainty

- There are no measurment that is excact because every measurement is a best estimation with margins of error.

- Despite of have the best estimation, for example, there are 39 cars in a parking lot is an exact number because it's a set of objects.

Absolute Uncertainty

A measurement of the uncertainty which is expressed in units. There are 2 methods to find it:

Method 1: Make at least 3 measurements and calculate the average. In the other hand, the absolute uncertanty is the largest difference between the average and the lowest or highest reasonable measurement.

               - For example: when calculating the avery of a few data eliminate the unreasonable data first:

1. 59                          The average is 59
2. 60                          I have eliminated 53 because it is a absolute uncertainty.
3. 58
4. 53
5. 59

 Method 2: Determine the uncertainty of each instrument

• When you are making a measurement, make sure you measure the best estimation you can (precision). In some real practices, you should estimate whatever the smallest segment that is possible on a instrument scale.
• For exmple, our rulers have the smallest scale as 1 mm, so that the best precision should break down to 0.1 mm. When you are measuring a thing, you need to see more carefully and precisely to be certain of the 0.1 mm differences.

Relative Uncertainty and Significant Figures

Relative          Absolute uncertainty

uncertainty =--------------------------------------

                        Estimated measurement

That's about what we have learnt today.

Kevin Wang