Which errors might occur when measuring length of object

Generally errors are classified into three types: systematic errors, random errors and blunders. Gross errors are caused by mistake in using instruments or meters, calculating measurement and recording data results. Measurement Error (also called Observational Error) is the difference between a measured quantity and its true value. It includes random error (naturally occurring errors that are to be expected with any experiment) and systematic error (caused by a mis-calibrated instrument that affects all measurements).