All experimental uncertainty is due to either random errors or systematic
errors. Random errors are statistical fluctuations (in either direction) in
the measured data due to the precision limitations of the measurement
device. Random errors usually result from the experimenter's inability to
take the same measurement in exactly the same way to get exactly the same
number. Systematic errors, by contrast, are reproducible inaccuracies that
are consistently in the same direction. Systematic errors are often due to
a problem which persists throughout the entire experiment.
Note that systematic and random errors refer to problems associated with
making measurements. Mistakes made in the calculations or in reading the
instrument are not considered in error analysis. It is assumed that the
experimenters are careful and competent!

How to minimize experimental error: some examples

|Type of Error |Example |How to minimize it |
|Random errors |You measure the mass of a ring three times|Take more data. Random errors can be |
| |using the same balance and get slightly |evaluated through statistical analysis and|
| |different values: 17.46 g, 17.42 g, 17.44 |can be reduced by averaging over a large |
| |g |number of observations. |
|Systematic errors |The cloth tape measure that you use to |Systematic errors are difficult to detect |
| |measure the length of an object had been |and cannot be analyzed statistically, |
| |stretched out from years of use. (As a |because all of the data is off in the same|
| |result, all of your length measurements |direction (either to high or too low). |
| |were too small.) |Spotting and correcting for systematic |
| |The electronic scale you use reads 0.05 g |error takes a lot of care. |
| |too high for all your mass measurements |How would you compensate for the incorrect|
| |(because it is improperly tared throughout|results of using the stretched out tape |
| |your experiment). |measure? |
| | |How would you correct the measurements |
| | |from improperly tared scale? |