My granddaughter, Aly G, was helping me organize my office. "This could be a lifetime career if you want it," I kidded her.

"That's OK, Grandpa," she replied as she held up a black leather case she had unearthed.

"What's this?"

"Wow!" I told her. "I've not seen that in dog's years. That is a slipstick. A Pickett N3-T Power Log Exponential slipstick, to be precise.”

"A slipstick?" I could tell by her look that she thought I was pulling her leg. Again.

"That's what us kool kidz called it back in the day. Properly speaking, it’s a linear slide rule. This was the way to calculate numbers before electronic calculators.”

She was looking more and more puzzled, so I figured I'd better show her how it worked. Amazingly, as I started handling it, I remembered how.

"Looks complicated," she told me.

"Well, it is more complicated than a calculator and nowhere near as precise. But it still has one big advantage over calculators: The slide rule forces you think about and understand the math and what you are doing in a way that no computer or calculator ever will. When you know how to use a slide rule, you really know how to do math.”

"In my troubleshooting workshops, I teach how important it is to understand a packaging machine before you can work on it. This is much the same thing.

"Would you like to have it?" I offered to my granddaughter. “I can teach you how to use it and you can impress your teachers.”

"Fiddlesticks on slipsticks!" she exclaimed. "Can I have this pocket calculator I found instead?"

Known as the Changeover Wizard, John R. Henry is the owner of Changeover.com, a consulting firm that helps companies find and fix the causes of inefficiencies in their packaging operations. He has written the book, literally, on packaging machinery (www.packmachbook.com) and is the face and personality behind packaging detective KC Boxbottom, the main character in Adventures in Packaging, a popular blog on packagingdigest.com.