Precision, Accuracy and Uncertainity

Precision: is a reproducible a measurement is compared to other similar measurements.

Accuracy: is how close the measurement comes to the accepted value

Low accuracy
High Precision

High accuracy
Low precision

High accuracy
High precision

Uncertainty
No measurement is exact; it is an estimate. Only when a set of whole objects are counted can we get an exact number ie. There are 25 cars in the parking lot.

Absolute Uncertainty
Is expressed in the units of a measurement instead of a ratio.

Method 1
The average of three measurements is calculates. (Remove unreasonable data)
The absolute uncertainty is the largest difference between the average and the largest or smallest reasonable measurement.
The answer is written as: The average plus or minus the biggest differnce
ie. 76.5 +- .2g

Method 2
Determind the uncertainty of of the innstruments used.
estimate to 0.1 of the smallest fraction of the measurment. ie. rulers smallest fraction is 1mm therefore we estimate to 0.1mm


Relative Uncertainty= absolute uncertainty/ estimated measurement
This ratio can be expressed as a percent

Significant figures tell us the relative uncertainty, since the last digit is uncertain!

http://www.mathsisfun.com/accuracy-precision.html

KP