Hey all, I'm new to the steel frame game and just bought a Touring bike in pretty good condition on Craigslist. I've noticed a small nick or ding on the seat tube that is pushed inward maybe a millimeter or two. I'm wondering at what point something like this qualifies as a "dent," and at what point do I need to actually worry/do something about it. Also, if you could explain why your answer is what it is, I'd appreciate that, as I'm always trying to learn more.

Pics are here; the ding is just under the horizontal scratch on the seat tube:



Thoughts/opinions?

Thanks guys!