Markup Dollars

I'm trying to understand markup dollars. I know this is not related to ProSpace, but my buyer has asked me to track markup and markdown events as they apply to the category, finelines and suppliers. I asked for the buyer's help to understand this better and was told to ask other vendors.
Markup and markdown event information can be pulled in DSS under MU/MD Scannable Item. Markdown dollars are easy enough to understand as they are defined as "amount of dollars lost due to markdowns" and show up as a positive number. However, markup dollars show up as a negative number, yet have many of the same "event descriptions" as markdown events. Is the store making money on these events ? If so, how ? I'm about to ask someone at a store, but thought I would ask Category Advisors first.