1964-D Roosevelt Dime D/D RPM

Both are machine damaged (Ejection damaged, but still machine damaged) and circulation damage on the upper serif. A point to not is that the overall size of the mint mark is reduced when you look at the west side of the upright on the first coin. The second coin shows the reduction on the overall size on the SE side of the mint mark. (Note the NE side of the mint mark? The lower area should have the same width, but the machine damage reduced the SE edge.)

Here is an illustration of a straight device. But consider this be a mint mark.

Note the lower left side of the coin in the illustration on the right side of the lower area? See the darker shaded side. That is where the device was altered and looking down from the top, it makes it look like a doubled device. But it isn't. The device was altered by machine damage. The overall shape of the device is there, just machine damaged. Hope this helps. If not, ask another question.

I'm glad it is helping. It is a tough subject for new collectors to get straight in their thinking. Then you discover the next one to test your education.

Questionable coins should be retained until you know for sure. I save extreme examples into tubes labeled with the name of why I save it. I save them for reference material. someone may ask a question about something and I can go to them to take images if they are a match for the subject. It makes them a quick find if I don't already have an image on that subject.