A ''sky chart'' program for optimizing Brewer zenith sky total ozone measurements at Rome Station is developed. It is applied to total ozone data at the Rome station, obtained by both direct Sun and zenith sky methods for the period May 1991 to March 1993, to compute new polynomial coefficients used in the calculation of the zenith sky total ozone values. These new coefficients are then utilized by the program to compute new zenith sky total ozone values. The percentage differences between (1) the zenith sky measurements computed using the old coefficients and direct Sun ozone data and (2) the direct Sun and the zenith sky total ozone values obtained using the new coefficients are presented. The new coefficients are also applied to some zenith sky (ZS) ozone data of Ispra. The results of the comparison between new ZS and old ZS values with respect to the corresponding DS measurements are presented. The new coefficients give more optimized zenith sky total ozone values than the old ones. ¿ American Geophysical Union 1995