Astrometric Limit: The maximum residual in the place of a reference star, specified in arc seconds.

天文测量误差极限：参考星位置对应的最大误差，用角秒表示。

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The precision of the static orientation is better than 20 arc-seconds, improved by an order of magnitude.

静态定位精度优于20角秒，比改造前的仪器提高了一个数量级。

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Degrees are divided into minutes (sixtieths of a degree) and seconds (sixtieths of a minute) of arc, so that there are 3, 600 seconds of arc, or arcseconds, in one degree.

ECONOMIST: A roadmap for planet-hunting

He missed the front end of a pair of one-and-one chances and was off on a jumper from just inside the arc with 29.2 seconds left and the score tied.

NPR: No. 2 Ohio State Beats Iowa State 78-75 On Late 3