Spline correction of a single OTF dump for the Galactic center project. Upper panel: master spline (shown as a dashed red line) used in the correction is also shown in dark blue in Fig. A.2. This master spline is scaled by a factor of −1.5, which provides a good match to the original data. Lower panel: residual after scaled spline subtraction. The weak broad emission seen between 20 and 70 km s⁻¹ in the spline-corrected spectrum is not visible in the original data.