There is a special tool designed to align the DR hanger. I've watched the local frame maker use one a number of times. He appears to be referencing the butt end of the tool in respect to the frame, but I don't understand how or what — or why except that he is straightening the hanger without any apparent fear of breaking it off. The last one he did for my was on a Gazelle. The hanger looked OK to me, but I asked him to look at it anyway. As it turned out, it was pretty much out of alignment. I think that it was Sheldon Brown who wrote that any bike that had been around for a while was pretty sure to have its hanger out of alignment.

As an aside ... I wish I could afford all the tools needed to service a frame — as well the knowledge to use them. I feel very lucky to live close to a craftsman for whom building frames and servicing them is a trade as well as an art.