You might want to check the Reports Library on Customer Source, I'm not sure if there's a report that includes Profit Margin, but it would be worth checking. It is possible to calculate a value and add it to various reports. I'm not sure that the number you are asking for really has any practical meaning though - you really need to look at actual sales prices, not just the "Price" field for the item - until an item goes onto a transaction, there's no profit to calculate. There are also some more complex calculations that can give you a better understanding of where you stand, such as Inventory Turns and GMROII
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Anyway, you can get almost any number you want out of RMS - some are harder to get to than others and some require you to take 'snapshots' at certain points in time, but you can get almost anything you want. Ask your reseller for help, or search the news group for hints on writing reports.