Hello Gord Lindsay,
Thank you for writing in.
There are three kind of power (Active Power,Reactive power and inspecting power).
This meter is used to measure the active power.
The calculating formula for active power is P=U*I*cos.cosφ represents power factor.
The power factor of pure resistive load (e.g.incandescent lamp, heater ) is nearly 1.
The power factor of inductive and capacitive loads is between 0-1.
So when you test the pure resistive load, P is equal to or near U*I; but when you test the inductive and capacitive loads (e.g.television,computer), P< U*I.
Various device is with various power factor.
We are not sure which power the house owner charge for the electricity.
So sorry we cannot provide suitable suggestion for you.
Best regards