Various energy transformations are possible. An energy balance can be used to track energy through a system. This becomes a useful tool for determining resource use and environmental impacts. How much energy is needed at each point in a system is measured, as well as the form of that energy. An accounting system keeps track of energy in, energy out, and non-useful energy versus work done, and transformations within a system. Sometimes, non-useful work is what is often responsible for environmental problems.