Physics a branch of science which analyses the nature by adopting physical quantities. To analyse the physical quantities and to get the relation between them, different laws, theorem, etc., are designed according the observation of nature. In the process of analysis measuring a physical quantity with respect to a specific unit is important.
While measuring the physical quantities there may be a chance of uncertainty to get accurate value. This uncertainty in the measurement is called error.
Due to presence of error in the measurement, we cannot measure exact or accurate value a physical quantity. But to minimize the error in the physical quantity and to get accurate value we can take average(arithmetic mean) of more number of readings. This average value of the physical quantity is known as true value.
Errors are of two types. Those are 1) Systematic error
2) Random error.
If the error in the physical quantity is either positive only or negative only every time then that error is called systematic error. i.e. always unidirectional.
This error may due to 1) Environment called Environment error
2) Instrument called Instrumental error
3) Person called personal error
4) Experimental technique.
For a measurement if we unable to say the cause of error then that error is called as random error.