4.03 Systematic errors

A systematic error is where a regular offset is produced between the measurement value and the true value. e.g. a ruler with a distorted scale (ie a calibration error - see later) that produces measurements that are always 10% larger than the actual true value.
Systematic errors can also be caused by consistently incorrect measurement techniques as well as calibration errors in a measuring instrument. Therefore systematic errors can be reduced by good measuring technique and the use of use of calibrated instruments (this is discussed in the next section).

Practical situations

Some types of errors are always systematic in nature while other types are always random. However some errors can be either random or systematic in nature. e.g. Parallax error is caused by not placing the eye in the correct position when reading a measurement from an instrument scale. If the eye is consistently placed say just below the correct position this will produce a systematic error. However, if the eye is randomly positioned when reading the scale this will produce random errors.

Combined random and systematic errors

In practice a measurement value is likely to contain both systematic and random errors. In this case repeating measurements with an adequate sample size would result in a distribution of values that varied randomly about a value that was offset from the actual true value. (The offset being the systematic error)