Paper 1 October/November 2019 PHYSICS (0625/11) IGCSE

A student tries to find the density of a metal block. First he measures the weight with a forcemeter (spring balance). Next he measures the sides of the block using a rule, in order to calculate the volume of the block. Finally he divides the weight by the volume to find the density.
The student has made a mistake.
Why does his method not give the density?