Timely testing of die on wafer reduces the cost to manufacture ICs. Calculating a variable influence indicator for the selected variable and repeating the steps for other selected variables enables an evaluation among the selected variables to determine their influence in the phenomenon. The at least one projection is located in the center portion of the vent disc and can be one projection, which extends from the vent disc at the center point of the vent disc. By connecting the energy exchangers electrically to the roadway system electricity grid, the energy exchangers may be powered by solar andor wind generating devices.