Calibration of vector magnetogram with the nonlinear least-squares fitting technique

To acquire Stokes profiles from observations of a simple sunspot with the Video Vector Magnetograph at Huairou Solar Observing Station (HSOS), we scanned the FeI lambda5324.19 Angstrom line over the wavelength interval from 150 mAngstrom redward of the line center to 150 mAngstrom blueward, in steps of 10 mAngstrom. With the technique of analytic inversion of Stokes profiles via nonlinear least-squares, we present the calibration coefficients for the HSOS vector magnetic magnetogram. We obtained the theoretical calibration error with linear expressions derived from the Unno-Becker equation under weak-field approximation.