At first glance, the mysterious carving looks a bit like a miniature electricity pylon with a latticed construction of uprights and grids. At the top is the outline of a misshapen cup which has a five-pointed star on one of the sides. Inside the cup shape, stacked on top of each other, are four diamond-shaped lozenges of different lengths and widths.

The crypt is part of an older structure on top of which the 15th-century chapel was built. It was used as a workshop during the chapel's construction and the scratching on the south wall seems to have been dismissed as a workman's sketch for one of the roof pinnacles.

"I can say with confidence this carving does not represent a pinnacle, or any three-dimensional church spire design," says Cowie. "This becomes obvious when you unravel the geometric layers."

Which is where he has the edge on most of us. Because where we see an electricity pylon or a badly drawn cup, Cowie sees a multi-layered, geometrically defined, mathematical template.