参考星：已知位置和/或星等的恒星，用于确定图片的底片常数和光度校准。
Reference Stars: Star with known position and/or magnitude, that are used to find the plate constants and photometric calibration of an image.
使用本类里的单选按钮，你可以选择使用底片常数的一次、二次或三次拟合。
Using the radio buttons in this section, you can set the software to use linear, quadratic or cubic fits for the plate constants. Small field CCDs usually require no more than a linear fit.
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