What is one of the potential sources of error when using Vernier Calipers in the experiment to measure the internal diameter and depth of the beaker?

A student performing experiment in laboratory took few values of internal diameter and depth of a cylindrical object. Based on the figures he determined, the mean measured internal diameter is $6.78 \mathrm{cm}$, the mean measured depth is $9.54 \mathrm{cm}$, and the Vernier Calipers exhibit a zero error of $-0.03 \mathrm{cm}$. The cylinder's computed volume will then be