Long story short, an inventory adjustment was made with an astronomical amount. I investigated it and found the cause, which was an item that was adjusted with a very large Rate. But, I also noticed something odd with a couple of the other items. Before the adjustment, there were zero on hand but they had positive Total Values. I ran an item saved search with Total Value and a formula that calculated the On Hand amount multiplied by the Last Purchase Price, which should be very close to an accurate value. I found that there were about 500 items that