What is a four fold ruler?

A four-fold ruler, often referred to as a folding rule or carpenter's rule, is a measuring instrument made of wood, metal, or plastic that can be folded into sections for easy storage and portability. Typically, it consists of four straight sections joined by flexible hinges, allowing it to be extended to various lengths. It is commonly used in carpentry, woodworking, and other measurement tasks where accurate lengths are needed. The ruler usually features measurement markings on both sides, often in both imperial and metric units.