Abstract: A test and diagnostic tool for stored program controlled telecommunications switching systems captures the occurrence and timing of "events" arising from subscriber actions and from actions which occur within blocks of software in the telecommunication switching system. Data related to the captured events as well as an indication of their location are stored in a large buffer memory. The stored data is then used to analyze the events for the diagnosis and correction of the cause of the fault as well as to recreate the same sequence and timing of events at a later period in order to test the corrections which have been made to ensure that they eliminate the cause of the fault condition.