The paper presents a usability study conducted with graduate and undergraduate computer science students, designed to evaluate the effectiveness of a software visualization tool named sv3D, and to provide necessary user data for the evolution of the system. Sv3D is a software visualization tool for comprehension of large software, capable of displaying source code and associated metrics in three dimensions.The participants in the study answered two types of questions: one set provided objective measurements to support the formulated hypotheses with respect to the accuracy and speed of the users answering questions using sv3D; the second set of questions provided subjective measurements that were used to support the evolution of sv3D.We formulated two null hypotheses with respect to accuracy and time respectively. The collected data supported one hypothesis and rejected the other.