Comparison Columns, need assistance interpreting documentation

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I want to build a report that compares aggregate chats weekly by queue, week over week, with additional columns indicating the percentage change +- between the weeks.

The documentation indicates that Comparison columns are the way to go, but the Help documentation might as well not exist, so lacking in simple clarity does it describe how to configure the report. Hey Oracle people, I've got an idea, why don't you include a link to a generic Incident report definition (we can have gratis) that uses this functionality? Then we vultures who really wish to showcase your product to our end-users don't have to spend an inordinate amount of time trying to find out how get it to work!!