Actually if you really want to know how you are doing indoors you might try to calculate your g/kwh. this will take into account the shorter or longer grow cycles, how much juice you use for environmental control, vegging time under lower wattage lights, and probably 100 other things. If you keep an accurate count of your weight over time, you should be able to compare that to your power demands by either putting your entire grow on a separate meter or calculating your power usage per electric appliance. Air conditioners are tough. IMHO, g/kwh has much more meaning than g/w. My power bill is the expensive part of my grow by far. My light mover is the best .036kwh/day value going. Very little added power, lots of extra yield. Of course it's only part of a system...