Complex sentence: Astronomer Geng Shouchang (耿壽昌) provided his armillary sphere with an equatorial ring in 52 BCE; by 84 CE the elliptical ring was added to the armillary sphere, while Zhang Heng's model of 125 CE added the celestial horizon ring and meridian ring.
Split into simpler sentences: Astronomer Geng Shouchang (耿壽昌) provided his armillary sphere with an equatorial ring in 52 BCE. By 84 CE the elliptical ring was added to the armillary sphere, while Zhang Heng's model of 125 CE added the celestial horizon ring and meridian ring.