the principle is the same as aquaero 4:

This function allows the calculation of the absorbed and emitted power
of up to two cooling circulations. A measurement of the water temperature at two points and the flow-measurement are required for the usage
of this function. Optimally these measurements should be in one circulation
and the temperature points should be at the supply and return lines of the radiator.
From the difference in temperature and the flow-speed the emitted heatenergy
is calculated.
To calculate the power, the heat capacity of water is needed, which is

4187 Ws/(kg * K).
Therefore an energy of 4187 Ws is needed to heat up 1 kg of water by 1 Kelvin.
Power= heat capacity * volumetric current („flow“) * difference in the
temperature
The power measurement is generally somewhat problematic due to the
inertia of the system, especially shortly after the start up of the system the
power measurement will show values that deviate from the real power.
Also every additive to the water will change the heat capacity of the
cooling liquid, which can not be taken into consideration in the calculation
of the aquaero. You should therefore regard the calculated value
only as interesting additional information.