With frequent measurement of the same dimension, the so-called. random error. E.g. measuring the dimension 5 cm, suddenly we mark 6 cm after a quick and inattentive look at the ruler. We will avoid this, when we put a marker at the measurement point on the measuring cup with a colored marker. Then a random mistake will be ruled out, and the marker can be easily wiped off after a series of measurements or washed off with a suitable diluent, e.g.. Nitro. Different measured dimensions can be marked with different colors.
