Abstract: A synchronizing circuit includes two switches for synchronizing the feeding of documents of a document feeder to the insert path of an insertion machine which is operative in accordance with a predetermined machine cycle to establish a given level of vacuum in a vacuum lines. The first switch closes in response to a given level of vacuum in the vacuum line and a rotary magnet driven by the insertion machine causes the second switch to close and then open at given machine cycles. The second switch and the first switch are in series with the document feeder; and, the second switch is operative to be closed and be held closed by the rotary magnet so that the document feeder is operative only upon the occurrence of both a given level of vacuum in the vacuum line and the predetermined proximity of the rotary magnet to the second switch.