A day seems to be what takes place between 2 reviews (morning and end of day review). dmx 
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Panda Planner, Monthly, Weekly, Daily post by Dakster Sullivan
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Towards the middle of the nineteenth century - thus somewhat anticipating the process of dissolution described above - Photography was invented. Only four aspects of this momentous invention will be singled out here, because they impressively illustrate the practice of "neg-anthropology". –– Flusser, Vilém. Vom Subjekt zum Projekt: Menschwerdung. 1. Aufl Juni 1994. Schriften / Vilém Flusser, 3. Bensheim und Düsseldorf: Bollmann, 1994, p. 18–22