may be used for: dimensioning the exchange and the telecommunications network; checking the system condition; finding system faults. The most important data produced by traffic measurements is the traffic intensity in the measured object. Core Network Planning and Optimisation Calculations in Erlangs are used in traffic measurements. The Erlang measurement is based on the true reservation time of the resource and the length of the results accumulation period. All of the reservation time is updated in the appropriate counter at the end of the call. For this reason remarkably large values in the Erlangs field are possible in a case in which there are many calls that have started before the results accumulation period but end in the results accumulation period. Traffic Observations Traffic observations produce real-time observation reports on individual calls and call attempts. Con- ditions for the traffic observation can be defined that, when fulfilled, cause an observation report to be generated. Some of the observation conditions are included in the exchange-specific settings that cannot be changed; e.g. reports on emergency calls are produced automatically. The data produced by the traffic observation are important when: analysing an exceptional operation of calls on a given circuit group; finding out reasons for failed calls (e.g. on a given circuit group); testing connections. Observations include: Circuit observation Number observation Clear code observation Combined observation Statistical observation All the observation types can be defined to be active simultaneously. If at least one observation condition is fulfilled, the system outputs an observation report on an individual call. Even if more than one observation condition is fulfilled for a call, only one observation report is generated on the call. 4.7.3 CS Core Network Audit A switching network audit is performed on the basis of measurements collected from a network element's own performance management counters. The collected measurements and observat