Fit of King curves to observed density profiles of open clusters residing at different heliocentric distances: small (Pleiades), medium (M67), and large (Berkley 58), shown from left to right. The curves represent the observed distribution of safe cluster members (dots), the one corrected for the residual background (circles with Poisson error bars), and the fitted King profile (solid red curve). Vertical lines indicate core radii (r_c, solid) and tidal radii (r_t, dashed). Blue lines indicate visual estimates, made earlier in MWSC, red ones are the current values of r_c and r_t derived from the profile fit. Horizontal bars indicate fit errors.