A nixie clock is a type of clock that uses neon gas-filled tubes, called "nixie tubes," to display the time. These tubes are shaped like the numerals 0 through 9, and the clock uses a different tube for each digit in the time.

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Nixie clocks were first developed in the 1950s and were popular until the 1970s, when they were replaced by digital displays. However, in recent years, there has been a resurgence of interest in nixie clocks, and they have become popular with collectors and enthusiasts.