One of My Favorite Stories

I heard a joke tonight about a slide rule that reminded me of my favorite story. First, the slide rule joke…

Several engineering students are taking a final. One of them is cheating and brought a slide rule to the exam.
“Hey,” the student next to him whispers. “Can you help me? What’s 3 × 6?”
The cheater reaches for his slide rule, and after a few seconds he replies, “19.”
“Are you sure?” asks the other.
The cheater again reaches for his slide rule, and after another few seconds he replies, “You’re right. It’s closer to 18… 18.3, to be precise.”

Yes, I know I’m dating myself by telling a slide rule joke. But honestly, I only know them from lore. I’ve seen them, and I understand how they work, but I’ve never actually used one for calculating.

Slide rules are a thing of the past, but math buffs have a fascination with them. One of my favorite stories is from Rick Wertheimer, perhaps the greatest math teacher ever from Pittsburgh. The following story, which may be apocryphal, is told exactly as I remember hearing it from Rick a decade-and-a-half ago.

Rick was getting a tour of a Hewlett-Packard facility. His guide shows him a room where there’s a bunch of old equipment — cathode ray tubes, punch cards, and lots of other outdated things. In one corner are two six-foot long slide rules that were designed for classroom use. Each has two hooks, and they were meant be hung at the top of the chalkboard for demonstration purposes — a teacher could use them to show students how the slides can be moved to perform calculations.

Rick says to his guide, “Can I have those?” After checking with some managers, the guide tells Rick that he can take them.

So, Rick takes both of them, one for his own collection, and one for his brother. On a trip to Washington, DC, he goes to his brother’s office at the Department of Defense, and on his shoulder he’s carrying the slide rule. As he walks in the door, the security guard stops him. Gruffly, the guard asks, “What’s that?”

“It’s a slide rule,” Rick says.

“Let me see it,” the guard says. When Rick hands it to him, the guard spends a few seconds inspecting it, and then starts moving the slides around.

Rick is a little puzzled by this. “What are you doing?” Rick finally asks.

And the guard says, “Clearing the data.”