How does it work?
The Profiteering tool - as it currently stands - serves as a gauge of how much profit you can gain by crafting items with all of the materials bought at the current average market price. The recipes are pulled from XIVAPI while the market prices are taken from Universalis. Without these two resources, this tool would not exist.
Keep the Lights On
I don't understand what all the numbers mean.
Let's start with the the potential gross. This number is the average of the past 5 sales for this item. Basically if you sold this item this is how much it would sell for.*
Next is the total cost. This is simply adding all of the red numbers you see in the "Mkt Cost" column. This is how much money you would be spending to craft the item using only materials from the marketboard.**
Last is potential profit. Plain and simple it's just the potential gross minus the total cost. This is how much extra money will be in your pockets after you sell the item. If this number is ever negative, you are almost definitely losing money by crafting that item.
* Due to the way player driven markets work, prices for things can fluctuate wildly due to normal quality vs high quality, no demand for the item meaning no new sales and prices have dropped dramatically since the last sale, or a handful of other things. Always double check your local marketboard for the current selling price and adjust the numbers accordingly. If I could use the current listings on the marketboards to gauge the price of things I would, but currently I've found that resource to be very unstable and slow, so I've opted for the less accurate, more stable, faster alternative.
**On top of the issues noted above, you also can't always buy the specific amount of materials needed. You might have buy 10 of 'Ingredient X' when you only needed 3 etc. meaning the actual total cost for you could be much very from what the tool says.