弧秒的英文：
arcsec

One second of arc movement is one thirtieth of a millimetre.
一弧秒的移动是一毫米的三十分之一。

If the diameter of the pupil is 6 mm the eye is able to separate 120 seconds of arc
如果瞳孔直径为6毫米，人眼可分辨120弧秒。

Until recent years, this tilt has increased by around 6 arc seconds, or about one-fifth of a millimetre each year
直到最近，塔身倾斜每年递增6弧秒，或约1;5毫米。