They Made A Tape For That
But they made a tape for that. I remember it distinctly as "the pink tape with the zig-zag ends which looked like it was cut with a pinking shears"; which meant it was very difficult to find on the Internet. (You're welcome, surfers who are also searching by such memories.)
I think my mom used that tape to make those curls by her ears which were oh-so-fashionable in the 60's. Those curls are called "guiche" -- and apparently each type of curl had a name. So now you can identify which kind of curl it was that that little girl has in the middle of her forehead. (And pray it's not The Fishhook!)
Funny thing is, I don't remember my mom using the tape to cut our hair... And our bangs were often a crooked mess, usually running in a diagonal line along our foreheads. Ah, good times.
Dad said she put a bowl on our heads to give us a trim and that she never bothered to monitor & straighten the bowl. I don't remember that. I just cringe when I see the photos.
If you pester me, I may make the time to find & scan a few for you.