The Scanning Long-wave Optical Test System (SLOTS) is a slope measuring deflectometry system that provides accurate measurements on ground surfaces. As it uses a thermal source, we can measure an optic during the grinding phase which allows us to correct figure errors when material removal is much faster. We have made improvements in SLOTS, such as the step-And-stare method, the ceramic rod, and the Gaussian fitting processing software, so that this system supports higher accuracy and resolution. As a result, SLOTS is an optical testing system that covers a huge portion of the fabrication process from the grinding to the figuring. It is a complementary solution for other metrology systems such as the laser tracker, SCOTS, and null interferometry. SLOTS can reduce the manufacturing time by producing ground aspheres that have low errors of the surface figure when polishing begins.