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Table 1.
Frequently used variables and functions.
| Quantity | Definition |
|---|---|
| i/m/e/z | Indexes for the star, frame, epoch, and sky field number |
| xi, m, yi, m | Measured star i position in the frame m |
| xi, 0, yi, 0 | Star i position in the reference frame m = 0 |
 ,  |
Geometric field distortion |
 ,  |
Displacement due to the proper motion, parallax, |
| and differential chromatic refraction (DCR effect) | |
| ξi, s | Star i model astrometric parameter, s = 1…7 |
 ,  |
Displacement of the star in frame m relative to frame |
| m = 0, corrected for the geometric field distortion | |
 ,  |
The same, averaged over some star subsample in the |
| sky field z at epoch e | |
 ,  |
Positional residuals for star i in the epoch e |
 ,  |
Systematic difference in the epoch positional residuals |
| of chips 2 and 1 at the division line between chips | |
 ,  |
The smooth component of the RCM in field z, epoch e |
 , 
|
Irregular component of the RCM in field z, epoch e |
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