Usage reports display the quantity of an item (or total of all items) used during a period of time. In order to calculate usage Backbar needs to know inventory counts at two different dates and how much of the item was purchased between those two dates. The usage formula is as follows:
Starting Inventory + Quantity Purchased - Ending Inventory = Usage Quantity
Therefore, in order to produce a usage quantity for each item, you must have done at least two inventory sessions in Backbar so we have a starting and ending quantity, and you must also have placed or entered your orders through Backbar.
Importantly, usage cannot be negative. When we calculate the usage for each of your items, if the usage is negative, we exclude that item from the report and any total calculations. The most common reasons why usage would be calculated negative are: