Measurement is the process of comparing unknown quantity with known or standard quantity.
Error is the difference between measured value and true value.
Perfect accuracy measurement is not possible. So, all measurement have some error.
There are Three types of measurement errors.
Human errors (gross errors)
Human error :- Human error or gross error are caused by humans by misreading of instruments, not using instrument in a way for which it was designed. Human error are also caused by calculation mistakes of humans.
Systematic error :- Systematic errors are caused by instrument by inherent inaccuracies of instrument or due to defective parts of instruments. There are two types of systematic errors one is equipment errors and second is environmental errors. Equipment errors are such as defective parts, mis-calibration of equipment and bearing friction etc. and environmental errors are such as change in temperature and change in humidity etc.
Random error :- Random error are caused by variation in parameter or system. By taking multiple times reading may help in minimising effect. Random error is always present in measurement. It is caused by fluctuations in reading measurement apparatus. Random error show different result for same repeated measurement.