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# Chapter 08 Types of Errors and Uncertainties in Measurement

The errors and uncertainties in measurement can be categorized as: systematic uncertainty, random uncertainty, mistake error and other errors.

1. Systematic uncertainty (SU)

Systematic uncertainty is related to the measuring instrument used. Each measuring instrument has its own, built-in uncertainty or error due to the way it is manufactured or calibrated. The accuracy of the measurement results in systematic error (SU) and is often referred to as the average uncertainty value (AUV) of the instrument. SU's have always the direction and often the same magnitude. In some cases corrections can be made to the data of the measurements to compensate for systematic errors. However, the best way of minimizing SU is to use better quality, more sensitive instruments, and you should not forget to check the zero error!


1. Instead of a ruler with systematic uncertainty ± 1 mm or ± 0.5 mm, it is better to use a vernier calipers with uncertainty ± 0.1 mm where possible.

2. Instead of using a 500 cm³ measuring cylinder with smallest graduation of 5 cm³, it is better to use a 50 cm³ cylinder with the smallest graduation of 1 cm³, if its volume is sufficient for the measurement.

3. Instead of measuring a current of, say, 23 mA with an ammeter having the range of 100 mA, it is better to use a more sensitive ammeter having a range of 30 mA.



When temperatures plunged to 32 degrees Celsius below zero in a small Canadian town, the local newspaper asked its readers to finish the sentence, “It was so cold that…” 
Here are some responses:
“…you could freeze an egg on the pavement.”
“…I had to go up and break the smoke off my chimney”
“…we opened the refrigerator to heat the house.”
“…when the police saw a bank robbery suspect and said, “Freeze!” he did.”
“... I let my dog out, and I had to break him loose from the tree.”

Reader's Digest, South Africa, June 1963


Do you like anecdotes, interesting and challenging problems, fun facts, puzzles, jokes related to metric system and measurement? Read them in the 2006 on-line edition of "SI Units, Conversion and Measurement Skills",186 pp.