المِزْوَلَة sundial

A sundial is a horological device that tells the time of day when direct sunlight shines by the apparent position of the Sun in the sky. In the narrowest sense of the word, it consists of a flat plate and a gnomon, which casts a shadow onto the dial. [Wikipedia] This is what was used previously to determine the timings for Dhuhr and Aṣr. The image displayed is of the مزولة found at masjid Al-Aqṣā.