The classroom overhead projector. Some of these were still in use last school year when I retired from the teaching profession. I had only had mine out of the classroom for a year, when I went exclusively with the smartboard and the E.
Exactly like my first pair of roller skates. You put your feet in them (with your shoes on), strapped them on, then tightened the toe hold with the key. "I've got a brand new pair of roller skates, you've got a brand new key.