Record keeper is a skill associated with the Bookkeeper appointed noble. It is used to determine how quickly the bookkeeper can take an inventory of the fortress and update the records to reflect any changes. It is trained by a bookkeeper doing the update stockpile records administrative labor.
As wealth and items are created or lost, e.g. by dwarves drinking up all your booze, the records will gradually deteriorate in precision, eventually ending up at the lowest precision rating. An assigned bookkeeper will therefore periodically update the records. How often depends on what precision he is trying to maintain, with the highest precision requiring the most work.
It is recommended to have your bookkeeper working around the clock, maintaining the highest precision level, even in small fortresses with relatively small stocks, so that when the number of items increases dramatically, less work is needed to catch up.