An extendable edge reference tool is disclosed. A first segment having a extending end and a receptacle end is provided. The receptacle end includes a coupling mechanism for joining a second segment using an over-center locking force to secure said second segment to said first segment. This tool provides for a useful continuous reference edge over extended distances through adjoining segments. Each segment is suitably compact to be easy stowed. The segments are useful individually. The segments can be joined to extend tool to lengths useful in common construction tasks.