hidden field to customers

any way to add a field that can be tracked in our systems when we create a invoice, to add what the cost of the item is vs the item sold cost and have it not printed when it comes to invocing a customer?

i do alot of sales and like to know what im making on any item, is there a way to add that into zoho invoice?? It would save alot of time on my end when im creating invoices to see how im doing on a month or weekly basis