Method and apparatus are disclosed for recording information on the accumulated usage of a group of trunks interconnecting two networks. The apparatus includes two usage records that are alternately designated primary and secondary usage records during successive ones of consecutive time periods. In response to a call on a trunk, the primary usage record is decremented by an amount representing the time interval between the start of a given period and the commencement of trunk use. During the period, each trunk connected to a network office is examined for use once during the period. When a selected trunk is found in use, the secondary usage record is incremented by an amount representing the interval of time in the previously occurring time period. When the secondary usage record has not been updated for the selected trunk, the secondary usage record is decremented by an amount representing the previous interval of time to adjust the secondary usage record for calls occurring prior to the trunk being checked for use. When a call is terminated on a trunk, the primary usage record is incremented by an amount representing the interval time between the start of the period and the termination of the call. In addition, the secondary usage record is incremented by an amount representing the interval of time in the previous time period when the trunk has not been checked for use. At the end of each period, the primary and secondary designations of the two records are exchanged for use during the next time period.