Types Of Error In Experimental Measurement

The two main classification of errors in the measurement of physical quantities are: Systematic Errors and Random Errors

Random Errors are minimised by taking more than one reading (let`s say n readings) and finding the average result. This can be statistically proven to reduce the variance of the measurement by a factor n For example:

Suppose you record 9 readings of time with a stopwatch of some event and using statistics and you work out the variance of these values and it comes to 27, then if you take these 9 values and find the mean result, the variance of all the results achieved taking many means (based on 9 readings) will only be 27/9 = 3 Vastly reduced.

Systematic Errors cannot be reduced in the same way because they arise from a fault (often unseen) in either the experimenter or the apparatus.The reason it cannot be reduced by taking an average is because a systematic error has a fixed direction. You are consistently either over or under estimating the actual reading. The classic example of this is a zero error on a voltmeter or ammeter. If, for example, the meter shows +0.1 Amps when zero current is flowing, then all readings when +current is flowing will be consistently OVERESTIMATED