The Supplier trends report, allows you to quickly compare your suppliers month over month over a set period of time.
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Click Supplier trends in the Reports box to the right of your the page.
For comparing there are two variables you are able to set. The first one is the Starting run this is the run you want to start comparing from. The second choice is the Value field, this is the data you would like to compare.
Once set you will see the comparison from the select run to current.