I wonder how local MQTT derives gas kWh?
The meter measures volume - it needs calorific value to calculate kWh. So presumably all kWh values returned by MQTT are estimates?
Further comment: so far as I can find out, the meter stores a fixed calorific value of 39.5.
I don't think this gets updated.
Jane told me today that we use the calorific value from the MPRN on the Glow service and it is fixed on the meter at 40 (or maybe 39.5) - so I think you are basically correct. There should be volume in the MQTT stream too - so you could DIY the kWh.
From my bill:
Usage = Units Consumed (Cubic Metres) × Volume Correction (for temperature & pressure) × Calorific Value (/m3 ) / 3.6
From what I can see from my bill history, the volume correction seems to be fixed (1.02264) but the calorific value has varied a bit. (currently 39.2).
Reverse engineering the local MQTT numbers suggests that glow assumes a calorific value of 39.5.