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In the past few years a number of variable angle spherical grating monochromators (VASGM) have been proposed and installed at Elettra beamlines. At present one of them (ESCAmicroscopy beamline) is operating, two (Spectromicroscopy and GasPhase photoemission beamline) are under commissioning, and one (Circulary Polarized Light beamline) is under construction. Although the experimental requirements of these monochromators are different, their control principles are the same. Approximately one year ago we started a project that aimed to provide a uniform and adequate system for controlling these monochromators. The paper deals with several frameworks of this project. First the monochromator software architecture is explained whereby the monochromator high level application options are explained. Instead of using extensive look up tables for the relationship between the energy and the angles of the mirror and gratings, we tried to develop an on-line mathematical model for energy tuning. An interesting feature of this model is that all monochromator data are parametrized which is important for the monochromator calibration. Much effort has been spent in order to understand the drive unit positioning behavior in the submicron scale which is non linear as a function of motor steps. As a result of this study some common drive unit mechanical properties were fixed according to which an absolute drive unit positioning control software is proposed. Finally we discuss some topics regarding the monochromator calibration and resolution optimization.