The 23-1990 Propeller Protractor is a 4-way precision instrument that measures angles directly between two surfaces, or any number of surfaces, such as setting a detachable blade type propeller on an airplane. Snug fitting circles are tooled to close tolerances that minimize the error and play found in other protractors. It has a matte finish to cut glare. This facilitates quicker and easier readings. The circle and plate vial are accurate to 45 minutes per two millimeters (mm). The Vernier reads to six minutes and can be set to read angles at any position in reference to any surface. Manufactured from aluminum and features a wooden handle.