1. A method of controlling a covering for a window according to both a timetable and a calendar, said covering having at least one attribute of function that is adjustable, said window being a feature of a building, said building designed for human occupancy, said building having attributes of geographic location and orientation, said window being subject to illumination from the sun, said illumination generally varying in many characteristics during both the solar year and the day in said geographic location, said location being within the usable broadcast range of a radio time standard signal, said signal being available for public benefit, said method consisting of both a) an initialization sub-method and b) a routine function sub-method, where the initialization sub-method preferably is prerequisite to the routine function sub-method, where the initialization sub-method comprises the operations of: a) accepting input of data defining the approximate geographic location of the installation, and b) registering said approximate geographic location, and where the routine function sub-method comprises the operations of: a) registering periodically the approximate day of the year, b) registering and updating repetitively the approximate time of day with respect to local celestial solar position, c) determining the approximate moment of local sunset for the approximate day of year, based on said approximate geographic location, d) allowing a human occupant of said building to make interactive changes to said adjustable attribute of the covering, and e) reverting the covering automatically to a previously determined value of said adjustable attribute, at a moment of time functionally related to said moment of local sunset as determined, thereby negating any recent interactive changes to said adjustable attribute, whereby a person can freely adjust and re-adjust a window covering during daylight hours, needing to perform no further action in order for the closing the window covering at dusk to occur.