Measuring projector: to distinguish with the traditional projector, this type of projector is called measuring projector. Its main role is to pass the product parts through the transmission of light into a magnifying projector, and then use standard film or grating ruler to determine the size of the product. Due to the development of industrialization, this measuring projector has become one of the most commonly used measuring instruments in the manufacturing industry. The method of periodic projection is divided into vertical projector and horizontal projector. According to the standard of its comparison is different and divided into contour projector and digital projector.