Translation:I bought a ruler at the university store.
I'm intrigued by the use of a comma here. Anyone have some insight on how it's being used? I know it's not mandatory, but I'm guessing it functions to offset the で from the 定規, maybe, so that it's clear that the で is setting context for the buying (I bought it AT the store) rather than the ruler (I bought the ruler that is AT the store).
It is not obligatory. No one I know says it that way. Just 店. It is very humble and self-effacing, and usually feminine. You would only say it under certain circumstances, like if you are a salesman talking to a shopkeeper about his wonderful shop because you want him to stock your product.