While on vacation in Sweden, Fred happened to run into "Cut-my-own-throat" Dabney while contemplating a portrait of Anders Celsius, the inventor of the temperature scale that bears his name.

Dabney said, "Fancy meeting you here! Hey, I see you're a fan of good old Anders! Seeing as how we go way back, I thought I'd give you a chance to own a piece of history that I happened to chance upon recently."

So saying, Dabney pulled out a sealed glass tube that was attached to a thin board. The board had some writing on it, and Fred could see that it was the standard centigrade scale, common to most of the world. The whole thing looked very old, and the script of the numbers seemed about 300 years out of date.

Not exactly thrilled to see this mendicant, Fred asked, "Really? Why would I be interested in that?"

"Because, me old chum," replied the slickster, "this mock-up of a Celsius thermometer was done by Anders himself. I'm willing to part with it for a mere five grand, and that's..."

"Yeah, I know, 'cutting your own throat'." Fred finished. "Listen, I don't have time for your rubbish, but I would gladly make the time to turn you in to the authorities for forgery."

How did Fred know it was a fake?