One cycle is from when & where it starts until it is back in the same position again. That would be, for example starting at the far left position, a sweep to the far right then another sweep back to the far left. Normally if those two sweeps take 8 seconds total then there will be two screen updates - one for each sweep - so every 4 seconds. They seem to be using some memory storage to buffer the antenna signal prior to being written to the display. That would allow the display sweep to be somewhat independent from the antenna sweep.
Last edited by Tinstaafl; 19th Mar 2014 at 20:16.