Easy readability, 7' standout, secure blade lock won't creep. Special Tru-Zero hook does double-duty as a pivot for drawing circles and arcs. Entire blade coated with Mylar polyester film for added durability, heat-treated spring stands up to repeated use, 16" and 19.2" stud center markings. Three-rivet, corrosion-resistant hook moves for accurate inside/outside measurements.