My daughter came into my office and asked to use a ruler. Sure top drawer of the Credenza. She opens it and picks up a slide rule, looks at it briefly and says what does this measure. Well it doesn't measure anything, it is a calculator. No really what does it do? It is a calculator. I answer. So she says: Here show me how to do 22 x 9. So I show her. Then come all the questions about how it works, and what else it can do. And of course it has been forever since I really used one. She lost interest, or so I thought, and then a couple hours later, I over hear her on the phone, telling a friend about the slide ruler and it multiplies and divides without batteries. .......