Panel a: observed CMD of NGC 2298; the arrow indicates the direction of reddening. The continuous lines are the axes (“abscissa” and “ordinate”) of the reference frame introduced in the procedure for the measurements of reddening variations. The position of NGC 2298 stars in this reference frame is shown in panel b where we draw the fiducial line of the MS as a dashed red line. Stars between the dotted lines (black points) have been used as reference stars. Panel C shows the rectified “ordinate” vs. Δ “abscissa” diagram.