One leaf falls each half-hour, at approximately 25 and 55 minutes after the hour. Having two sets of leaves for each hour also allows the clock to alternate between 12- and 24-hour display, every half hour, like this: 12 am, 0 h, 1 am, 1 h, 2 am, 2 h. There are two of each hour, like this: 12 am, 12 am, 1 am, 1 am, 2 am, 2 am. These leaves have hour numbers printed on them. The slower wheel has connected to it a similar ring of leaves, only there are 48 leaves on this ring. This ring is put into position and rotated so that one page falls each minute, showing a new number for the minutes. The "book" is opened vertically, and its pages form a ring. ![]() On the leaves are printed numerals so that, when a person holds two adjacent leaves apart like an open book, the two open leaves spell out a numeral, and flipping a leaf down increases the number shown by 1 unit. The faster wheel has connected to it a ring of 60 flat plastic leaves. The small hook which retains the hour leaves until the top of the hour can be dimly seen, retracted, in the inset. ![]() This is a synchronous electric clock which is kept to the correct time by the 50/60 Hz AC power grid. The narrow numbered wheel and knobs on the left are the alarm mechanism. The inset shows the metal tab holding back the top flap. Mechanism of a split-flap alarm clock, removed from its case.
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