I need to replace a ballast and I have a spare, but it is not the same size. The current ballast is a 250 w HQI selectable and this is a 400 w selectable. It does not have the wattages marked on the dial. 1. Can I use it and try to match the dials position with my other selectable 400 watt ballast? 2. Does anyone how to gauge or measure the output of the ballast? If so what wattage is a 250 watt HQI overdrive to?