A community is considering switching from coal-fired power plants to using wind energy to generate electricity. In order to decide what type of wind turbine is best for the area, an investigation was conducted to compare the amount of electricity generated using different blade lengths. A series of wind turbines were assembled at a location near the community and tested to compare the amount of electricity each wind turbine could produce. Care was taken to make certain that each turbine was positioned to be exposed to the same wind direction and speed. (h) Other than positioning the turbines to be exposed to the same wind direction and speed, identify one variable that would have been held constant in the investigation.