Dan Graham
«Present Continuous Past(s)»

The mirrors reflect present time. The video camera tapes what is immediately in front of it and the entire reflection on the opposite mirrored wall.
The image seen by the camera (reflecting everything in the room) appears eight seconds later in the video monitor (via a tape delay placed between the video recorder, which is recording, and a second video recorder, which is playing the recording back).
If a viewer's body does not directly obscure the lens's view of the facing mirror the camera is taping the reflection of the room and the reflected image of the monitor (which shows the time recorded eight seconds previously reflected from the mirror). A person viewing the monitor sees both the image of himself or herself of eight seconds earlier, and what was reflected on the mirror from the monitor eight seconds prior to that–sixteen seconds in the past (the camera view of eight seconds prior was playing back on the monitor eight seconds earlier, and this was reflected on the mirror along with the then present reflection to the viewer). An infinite regress of time continuums within time continuums (always separated by eight-second intervals) within time continuums is created.
The mirror at right angles to the other mirror-wall and to the monitor-wall gives a present-time view of the installation as if observed from an «objective» vantage exterior to the viewer's subjective experience and to the mechanism that produces the piece's perceptual effect. It simply reflects (statically) present time.

(Doug Hall/Sally Jo Fifer: Illuminating Video – An Essential Guide to Video Art, New York, 1990, p. 186)