Saturday, October 30, 2010

Accuracy & Precision

Accuracy : how close the measurement comes to the accepted/real value

Precision : how reproducible a measurement is compared to similar measurements

No measurement is exact. Its just a estimation. It may still has some degree of uncertainty

~Absolute uncertainty = largest difference between the average and the lowest/highest measurement
Method 1 : Calculate the average(at least 3)
For example : 8.3, 8.5 & 8.1
Average = 8.3
Absolute uncertainty = 8.5 - 8.3 = 0.2
It will recorded as 8.3+/-  0.2

Method 2 : Determine the uncertainty
Measure the best precision that you can. You should estimate to a fraction 0.1 of the smallest segment on the instrument scale.
For example :
Thermometer  Smallest : 1degree,   Best precision : 0.1degree,   uncertainty+/- : 0.1degree

~Relative Uncertainty = Absolute uncertainty/Estimated measurement
                                    

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