An efficiency of assigning weights to star observations at equal heights is studied. The imperfections of standard method for weighing based on deviations of stars from mean almucantar obtaining from observations of a star group are considered. The possibility of the evaluation of the quality of observations of individual star on the basis of the convergence of its height deviations from conditional almucantar is studied. By the example of some sets derived from observations with a prismatic astrolabe in Poltava we studied some statistical characteristics of star height arrays (trends and dispersions) and carried out a reprocessing of sets with taking into account the weight factors depending on individual deviations of star heights from the curve of systematic variations of the height for this star. It is established that systematic components of height variations for majority of star differ from modelled ones (on the basis of the Earth's rotation parameters data) by a constant value; the varying differences are less than 0.1"; dispersion of stochastic component is about 0.26" and slightly depends on the magnitude of a star; the distribution of stochastic component obeys Pirson's law; application of our weighing method improves the convergence of latitude sets by not less than 15 %.