Power Genius devices report both total power and mean power. The total power is reported in kWhrs (kilo watt hours) and same as the value reported on an electricity bill.
The total power can be calculated by multiplying the mean power by the amount of time in hours. For instance if a 1kW heater operated for one hour, the total power would be reported as 1kWhr. If the heater operated for half an hour the total power would only be 0.5kWhr which is calculated by multiplying 1kW, which is the mean power, by half an hour. The mean power can be thought of as the rate you use electricity while the total power is the amount of electricity used. Compare this to a car that consumes fuel. The car's fuel consumption is measured in kms/l. If the car is driven at the same speed it will do say 100km per litre. This value is the same regardless of how far the car travels. If the car travels for 100km it will consume one litre of fuel which is the total fuel consumed. If the car travels only 50km it will consume 0.5litres of fuel but the average, or mean, fuel consumption will still be 100km per litre.
Power Genius nodes report power usage over an interval of time. The total power reported is the amount of power used over the interval. A five minute interval is 1/12th of an hour. A node reporting a mean power of 3kW over 5minutes would report the total power as 0.25kWhrs over 5 minutes which is 1/12th of 3kWhr where 3kWhr is the total power over an hour.
For some devices the mean power doesn't change much while for others it may vary a lot just as a cars fuel consumption may vary depending on how much you use the accelerator.