A lot of books about typography start with the way calligraphers form letters with pen and ink. This is of course related to how type designers design type, but when people were first printing from metal type, what they did didn't have very much to do with writing with a pen.
Instead, they made the type from a "punch", which was a metal image of the letter, and one of the ways they made the punch was with a "counterpunch", which might carve out a blank place in the middle of the letter. They might use the same counterpunch for the middle of a, g, p and d.
This book has all the information its author could come up with for how the great type makers of the 16th century worked, and also some observations about how type design has changed with computer programs for automating some of the work of type design.
I'm always fascinated by the fact that just about anything I'm interested in (cooking, music, literature...) turns out to have been changed in major ways by how people did it in the 16th century. Printing is another example of that.