Want to know how much money you've made off an item?
First, a Custom Attribute to you inventory items called 'Original Cost' (or something similar).
Next, add your 'Gross Revenue' custom column.
Finally, move the Attribute Column 'Original Cost' and 'Gross Revenue' columns side by side so you can see how much you've made vs the original cost for the item.
Pro tip: You can also use the Date Filters to show you your Gross Revenue over a given period.