ACWTIME is the duration of time an agent spends in ACW that is associated with an ACD call. I_ACWTIME is the sum of time an agent spends in ACW during the collection interval. This includes time that is associated with the ACD call and the time an agent spends in ACW that is not associated with an ACD call. I_ACWTIME also accounts for the extra time an agent spends in ACW for which an association with the prior ACD call cannot be established.