If the length of the rod is exactly 1 cm, when an observer records the readings as 1.0 cm, 1.00 cm, and 1.000 cm, then the measurement which measures 1.000 cm is most accurate because it has more number of significant figures and the instrument which measure this data has less least count than the other. The instrument which measures the length of the rod 1.0 cm can measure two digits after the decimal and the third instrument which measures lengths 1.000 cm can measure three digits after the decimal. So, the third instrument can measure accurately.