Math teacher Sherry Read's classroom is a total mess. The students are gone for the summer, and light fixtures dangle from the ceiling. The floor has a layer of dust. Down the hallway, workers make a racket while they renovate the school, which dates back to the 1890s. They're working in what has become an archaeological site.

A construction crew at the Oklahoma City school made a startling discovery earlier this month. They found old chalkboards with class lessons that were written almost a century ago, and chalk drawings still in remarkably good condition. So Read doesn't mind the mess. In fact, she's amazed.

"It's like touching history, like being a part of what was going on during the day," she says. "It's just remarkable and mysterious, trying to figure out what some of this was."

The biggest mystery is an old multiplication wheel. It's a circle with factors on the inside and other numbers on the outside. No one can figure it out.
Image of the wheel here at link: