紀限儀，是古代中國用於測量60度角以內，任意兩天體的角距離的天文儀器。 自秦朝後「數以六為紀」，故亦稱六分儀，西方亦有類似功能儀器。
The Sextant is an ancient Chinese astronomical device used to measure the angular distance between any two celestial bodies within a 60-degree angle. After the Qin Dynasty, it was referred to as “sixth instrument” due to its association with the sexagenary system. Similar instruments with analogous functions also existed in the West.