I thought I'd post an example of
Machine Doubling on a 1994-P quarter that I found today in my pocket change. In addition to the pictures posted here, the whole obverse profile (especially the nose and forehead) is doubled, and on the reverse most of the left wreath, eagle's neck, head and wings are doubled, also.
Here's the date... all digits are doubled, especially the "1" and "4" !!

The "T" in TRUST is also doubled .... along with all the other letters (especially the "N")....

On the reverse, check out the back of the arrow feathers and the wreath...

Also, the "U" in UNUM is strongly doubled....

This is just an example of
Machine Doubling you might find all on one coin, not to be confused with hub doubling or "true" double dies.
HTH,
Rick