Oct,31--Accuracy and Precision

Precision: is how reproducible a measurement is comparing to other similar measurements (approximately to other numbers).


Accuracy: is how close the measurement (or average measurement) is to the actual value.

Measurements and Uncertainty

- Measurements are only best estimates. Every measurement has some degree of uncertainty.
(Except for numbers like 5 people, three bags, etc.)

Absolute Uncertainty
-The uncertainty expressed in the units of measurement, not as a ratio.

How to calculate the absolute uncertainty?

♥Method 1: Measure for more than 3 times, then calculate the average.(You may omit the measurement that is most different from others.) The absolute uncertainty is the largest difference between the average and the lowest or highest reasonable measurement.

♥Method 2: (determine the uncertainty of each instrument) When making a measurement, always measure the best precision, which means you should estimate to a fraction 0.1 of the smallest segment on the instrument scale.

Relative uncertainty and significant figures

*Relative uncertainty=absolute uncertainty/estimated measurement

(The number of significant figures indicates the relative uncertainty)