On 16/11/2020 18:07, Andy Burns wrote:
Roger Mills wrote:

Dave Liquorice wrote:

The CurrentCost one http://www.currentcost.com/products.html has a
TTL serial output

I got one of them free from e.on (together with USB/serial converter cable)

Is that showing true watts, or simply volt-amps

You don't get billed for watts, just volt-amps

No, you get billed for volts * Amps * Cos(phase angle between them).
If you stick a large lossless capacitor across the mains and draw loads
of current it will not cost you anything.