In telecommunication, a call-second is a unit used to measure communications traffic density. Note 1: A call-second is equivalent to 1 call with a duration of 1 second. Note 2: One user making two 75-second calls is equivalent to two users each making one 75-second call. Each case produces 150 call-seconds of traffic. Note 3: The acronym CCS (Centum Call Seconds) is often used to describe 100 call-seconds. Note 4: 3600 call-seconds = 36 CCS = 1 call-hour. Note 5: 3600 call-seconds per hour = 36 CCS per hour = 1 call-hour per hour = 1 erlang = 1 traffic unit. Hence: