The method to determine the globular cluster center. From left to right: a zoom into our HST/ACS image of NGC 6388 (used to derive the CMD and luminosity profile for the cluster) with the over-layed grid of trial centers. Around each trial center, differential stellar counts and stellar luminosity were computed in two opposite wedges extending 15′′ in radius (middle panel). A minimization of the residuals, as shown in the contour plot (right panel) determines the center to within 0.2′′. The distances between the contours vary between 40−70 stars for the star count methods.