A paper handling apparatus including: feeder stations for feeding documents to a conveyer; a collator for collating documents into packs, and collating packs into groups of documents; an inserter module for inserting each group into an envelope; a monitor which monitors the cycling and working times of sections of the inserter module; sensors for determining at least one of: a first desired gap being the minimum gap between trailing edges of consecutive groups, a second desired gap being the minimum gap between the trailing edge of one pack and the leading edge of the following pack a third desired gap being the minimum gap between the trailing edge of one group to the leading edge of the following group; and a controller for controlling the feeder stations to achieve at least one of the desired gaps.