Resulting RMS residual in arcseconds

This is the uncertainty (or error), in any direction on the sky, in the determination of the RA and Dec of the object (e.g., asteroid). It is expressed in arcseconds. In other words, the object is most probably within a circle of this radius centered on the RA and Dec determined for the object.

If this value is large (10's of arcseconds, or more), it is likely you made a mistake in entering your star data (sky coordinates, or x,y pixel coordinates), or you made a mistake in your identification of stars in the image.

Technically, this value is the root-mean-squared (RMS) difference between the actual RA, Dec position of the stars used to determine the x,y-to-RA,Dec transformation and the RA, Dec coordinates determined for these stars by the transformation.

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