A subject is connected to a monitoring system and videoed while being monitored. The monitoring system receives raw data from the subject and processes the raw data into waveform data, and transmits the waveform data to a marking device. The marking device simultaneously marks the waveform data with a waveform reference point and causes a light emitting diode to flash in the video, thereby creating a video reference point. A computer program locks the waveform reference point with the video reference point and thereby synchronizes the waveform data with the video.