Sometimes, it's not obvious why a particular item has appeared on your purchase order (for example if you've created a purchase order based on reorder levels and restock points).
Inside the purchase order contents, there's a little button designed to help you with this:
If you click this button, a popup will appear, detailing how the quantity was calculated:
In this instance, only one unit was required to meet restock level and reorder point requirements, but the manufacturer supplies these in boxes of 10, so an extra 9 units were added.