A controlling node for a cell in a cellular system, arranged to measure a performance indicator of the communication between the node and at least one user and to aggregate the measured performance indicator for at least one user over an amount of time. The performance indicator is measured as the amount of data bits successfully transferred as data blocks in uplink and/or downlink between the controlling node and the at least one user during said defined amount of time, divided by the number of smallest physical resources in the system in terms of time and frequency used during said defined amount of time. One or more predefined combinations of one or more data blocks and one or more said smallest physical resources in the system is/are excluded from the aggregated measurement.