Option for simple calculated series options based on entities?

[TommySharpNZ]

I am trying to create a power usage donut and need a calculated value for "Other Devices" that will help me visualise devices which I do not track individual power usage on.

I've not seen a way to add or subtract entity values so maybe this could be a new feature if it's not already possible?

Something like this...

- entity: sensor.electricity_usage_w - sensor.athom_plug_v2_01_energy_power - sensor.athom_plug_v2_02_energy_power name: Other Devices