in a momentary power source voltage value the data acquisition interface 21 may be an integral part of or connected to a terminal power consumption evaluation processor 22 for forwarding and processing of the terminal current value and the momentary power source voltage value from here on the terminal power consumption evaluation processor 22 is referred to as the processor 22 the processor 22 may be a personal computer for example a laptop computer or a dedicated embedded computer a momentary terminal power consumption value can be established by multiplying the momentary power source voltage value with the momentary terminal current value by the processor 22 alternatively if the power source 17 voltage is not measured the momentary power consumption is determined by the momentary terminal current alone the momentary power consumption is integrated during a user activity 2 a 2 m power consumption measurement to obtain a user activity power consumption measure during or following the test of step 6 in the process described above the user activity power consumptions are stored 7 in a data structure 8 by the processor 22 a user activity power consumption measure is treated as the sum of its terminal power consumptions measures after a set of user activity power consumption measures have been established the processor 22 is arranged to calculate the terminal activity power consumption measure.