Calculation of rest of house power (Kwh)

Hello All,

I have installed my home assistant and I measure the consumption using a bticino living now power meter.
I would like to monitor the power consumption for the plug not monitored and to do this I thought to subtract the monitored plug consumption (I already created an helper with “all rooms monitored consumpion”) to the total consumption (the one that monitor my total house consumption).
Can you please suggest how I can do it?