Prep Item costs are recalculated automatically by Compeat when you open either the Prep Items screen, the Produce Prep Items screen, or the Valuation Counts screen. This is so that, in the typical rhythm of events at a restaurant, a daily recalculation based on the changing costs of ingredients is made. Once Compeat has done an automatic recalculation in a day, it will not do it again until the next day.
Another way to update costs is to select this command. Thus, you can manually recalculate all prep item costs whenever you choose. For example, if you need your costs to be updated immediately to ensure you have the latest prep item costs before doing a valuation count posting, just run this utility.