Allow exclusion of used items in the critical stock calculation

When looking at "items at critical level" there are a large number of durable items that are shown as below critical level despite having healthy stock levels due to a small quantity of used items being stored. In our workshops we only ever have a small quantity of used items before they are utilised on Jobs; this leads to the critical stock level function being largely useless as over 95% of the items classed as at critical level in our vending machines are actually well stocked with new items. (See attached image for key examples)

If it were possible to allow the critical stock level to ignore the stock level of used item it would allow the functionality to be used in stock management.