On Thu, 17 Sep 2009 13:33:02 +0100, Bill R wrote:

I spoke to someone from the 'Electricity Efficiency Team'. He tried to tell
me that the reading was an average reading over any hour. I pointed out
that the measurement unit was watts not watts/hour.

Watts/hour is meaningless. There is nothing wrong with averaging watts over
any particular time period, if that's how the device is designed to operate.
It obviously will underread for the first hour and obviously won't react
instantaneously to changes in load.

He then went away to
the manufacturers who came back with the concept of 'power factor'

That's manufacturer's talking ********.

My schoolboy knowledge of a watt being voltage divided by amperage is
obviously wrong.

It certainly is, seeing as watts = volts x amps.
Volts divided by amps is ohms.
Are you Dave Plowman? He gets simple formulae such as this completely
arse about tit. (He thinks power = energy x time .... it isn't)

I cannot get my head around the concept of power factor

It's a measure of the phase difference between voltage and current.
Real power is volts x amps x cos(phase difference)
and power factor = cos(phase difference)