There are three main errors that can occur in most situations when calculating results, and these are the easiest to explain:.
1. Systematic error - errors "built in" due to the method selected (also called determinate error). It can be eliminated. .
2. Random error - random, uncontrolled errors (also called indeterminate error). It cannot be eliminated, and affects both accuracy and precision. .
3. Gross error - error due to incompetence.
Systematical error.
If we were to measure a tabletop, it may happen that our meter stick was slightly miscalibrated at the time of manufacture, so it gives consistently large results. We would not be able to correct for such an error by repeating the measurement. We would instead have to recalibrate the meter stick. Sometimes we are not able to do the recalibration, but are assured by the manufacturer or by some other means that the meter stick agrees with a precise standard to within an error of say 0.005 m. We could then quote the result of a measurement of the tabletop by saying it is 3.158 ±0.002(statistical) ±0.005 (Sytematical) m, identifying separately the two sources of error, the first source of error being statistical, and the error we are interested in being the systamatical error.
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Random error is simply a fluctuation of the measurements taken, if we take the example above and measure the table a hundred times, the random error can be minimised as a mean result is gained, as we know the systematic error will not change.
However these random errors can affect the accuracy and precision of the experiment.
If there were several measurements taken of the table, like we said the random error would decrease, as a mean pattern becomes apparent. However if their were a number of different people taking the measurements, the mean across a period of time may not become apparent, and if we were to plot the actual measurements, the graph you would probably see would be cycling through a number of different points, due to many external factors including operator technique, and environmental changes.
