The Accusplit Survivor S3MAGXLBK Stopwatch has great economical features and functions designed to give you professional timing in an affordable manner. The S3MAGXLBK operates on the Watch Company Operating System (WOS 2.5) used by most watch manufacturers, which employs a two-button system. The right button is used for start and stop, the left for split and release. The S3MAGXLBK stopwatch features cumulative-split timing. The cumulative (CUM) time is the capture of elapsed time to current event and consists of all splits beginning to end. The split time is the interval of time measured from the start of the timing to the next pause of time.