The Virtual Reality System is a piece of technology in Crisis Core -Final Fantasy VII-, which allows a test subject to interact with prepared data in a virtual environment. Any variety of virtual simulations can be created, such as all sorts of monsters, so it is mostly used for Shinra Electric Power Company army training and special experiments. However, since the wounds one receives when using the Virtual Reality System are real, there is danger involved with its use.
The goggles Zack wears in the game's opening were equipped to collect data directly from his body. Thus, because all of the details of the training must be able to be measured in real time, they must be worn during SOLDIER Class promotion tests.
The Crisis Core Complete Guide reveals that Biorhythm-Testing Materia Equipment is designed to work in the Virtual Reality System's cyberspace and works in tandem with the examination equipment. To facilitate Professor Hojo's observations, a compatible Fusion Chamber had to be built. The Complete Guide further states that as it is full of highly specialized equipment, the amount of money needed to repair it after being damaged by Sephiroth, Genesis and Angeal after their training exercise, cost an amount equal to 24 months worth of Zack's SOLDIER 1st Class salary.