Recently I visited Maison de l'Outil (the house of tools) in Troyes, France. This is a museum containing tools from all trades, from coopering to butchering, and lots of woodworking tools. There was one tool that intrigued me more than the others, that being what appears to be a marking tool, possibly an early rafter square. The tool itself appeared to be separable to allow marking of different angles. While I would like to build one of these for myself, I'd like to know what it was used for. Any ideas?