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ularities serious enough to affect service, will routine tests be instituted totrace the trouble. Faults observed by subscribers or operators will in mostcases be reported to the wire chief's desk. Various forms of automatic routiners,such as traffic route testers, exchange testers, tariff testers, line testers.and register testers, are available.The maintenance program can be classified as follows:Syd5000 nos.Fig. 2Local exchanges in Aarhus area1. Localization of faults (traffic tester, centralograph, inspection, routinetests).2. Clearing of faults.3. Cleaning of exchange equipment.The first two categories of maintenance work are performed by exchangemaintenance men assisted by trainees. Cleaning of exchange equipment isdone by women.Maintenance of Local ExchangesThe quantity of maintenance work is dependent on the size of the exchange,the number of lines in service, traffic density, and the like. Some data ofinterest pertaining to the local exchanges in the Aarhus area are given intable 1.Table iNo. subs,at 1/1/56SL (outg. + inc.)erlangs/100 subs.Busy hour trafficI GVeilangsII GVerlangsOutg. callsper sub.and dayCentrum ....VestBrabrand ....Risskov ....Skaade ....Syd14,8022,3935601,6671.0743,5867.04.94.64.85.14.949510120.764.843.21435189.06.56.05.86.25.924,0826.28685187.9The number of calls per subscriber and day is calculated as the Monday—Friday average. On a day with heavy traffic the originated calls per subscriberon the Centrum exchange may number about 11, and incoming calls roughlythe same.The holding time on originating calls averages 105 sec.» » » » incoming » » 1 15 »Register holding time is 10 »The busy hour calling rate is 11.5 for originating calls and 12.5 for incomingcalls.In accordance with the customer's specifications the equipment was designedfor a congestion of 0.2 % in every switching stage, with total congestion notexceeding 1 %. At 10% overload the congestion must not exceed 1 % perswitching stage. The filling grade for the individual thousands groups, however,is not especially high, and only on rare occasions does the volume oftraffic approach that for which the equipment was designed, so that congestionseldom arises.As already stated, now that troubles associated with the installation andrunning-in period have largely disappeared. J.T.A.S. has confined routinetesting to the Centrum exchange and only uses it there as required. The