Random errors are determined through statistical analysis based on following assumptions :

• Small variations from the mean value occur more frequently than large ones.
• Positive and negative variations of the same size are about equal in frequency, rendering their distribution symmetrical about a mean value.
• Very large variations seldom occur.

Thus, to eliminate random error in a measurement, observations are repeated for number of times. The mean (average) of observations is considered to be the true (or estimated) value of the measurement. Normal or Gaussian distribution typifies the distribution of samples of any measurement.

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