A traveling microscope is an instrument for measuring length with a resolution of about 0.05 -0.1 mm. It is composed of a microscope mounted on two rails fixed to a supporting structure. The position of the microscope can be varied coarsely by sliding along the rails, or finely by turning a screw. Position of the microscope is read by a vernier. Purpose of the microscope is to aim at reference marks with much higher accuracy compared with bare eyes.