Developed in England during the 17th and 18th centuries, minute repeaters sound the time in hours, quarters and minutes—hence their name. Repeaters served a practical purpose: telling time in the dark. When streetlights were rare and matches and candles precious, chiming watches were a logical solution but not a simple one.
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A minute repeater chimes different sounds for the hours, the quarter hours and minutes. The lowest tone—dong—is for hours, the highest tone—ding—is for minutes and a combination of both—ding-dong—counts quarter hours. If the slide is pushed at 12:59, the sounds heard are: 12 dongs for the hour then three ding-dongs for the quarter hours followed by 14 dings for the minutes.
How delightful! Watches with these complications are very difficult to make and are hence very expensive. Here’s a video of Patek Philippe’s entire line of minute repeaters. Cursory Googling tells me that the nine watches on the table are worth a total of ~$5.4M.