A binary clock is a

clock A clock or a timepiece is a device used to measure and indicate time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month and t ...

that displays the time of day in a binary format. Originally, such clocks showed ''each decimal digit'' of sexagesimal time as a binary value, but presently binary clocks also exist which display hours, minutes, and seconds as binary numbers. Most binary clocks are digital, although

analog Analog or analogue may refer to: Computing and electronics * Analog signal, in which information is encoded in a continuous variable ** Analog device, an apparatus that operates on analog signals *** Analog electronics, circuits which use analo ...

varieties exist. True binary clocks also exist, which indicate the time by successively halving the day, instead of using hours, minutes, or seconds. Similar clocks, based on Gray coded binary, also exist.

Binary-coded decimal clocks

Most common binary clocks use six columns of LEDs to represent zeros and

ones Ones may refer to: * ''Ones'' (album), by Selena, 2002 * The Ones, New York electronica group * "The Ones" (''30 Rock''), an episode of ''30 Rock'' * In music, single bars of alternating solos (as in "trading ones"); see Rhythm section#Musical r ...

. Each column represents a single decimal digit, a format known as

binary-coded decimal In computing and electronic systems, binary-coded decimal (BCD) is a class of binary encodings of decimal numbers where each digit is represented by a fixed number of bits, usually four or eight. Sometimes, special bit patterns are used fo ...

(BCD). The bottom row in each column represents 1 (or 2⁰), with each row above representing higher powers of two, up to 2³ (or 8). To read each individual digit in the time, the user adds the values that each illuminated LED represents, then reads these from left to right. The first two columns represent the

hour An hour (symbol: h; also abbreviated hr) is a unit of time conventionally reckoned as of a day and scientifically reckoned between 3,599 and 3,601 seconds, depending on the speed of Earth's rotation. There are 60 minutes in an hour, and 24 ho ...

, the next two represent the

minute The minute is a unit of time usually equal to (the first sexagesimal fraction) of an hour, or 60 seconds. In the UTC time standard, a minute on rare occasions has 61 seconds, a consequence of leap seconds (there is a provision to insert a n ...

and the last two represent the second. Since zero digits are not illuminated, the positions of each digit must be memorized if the clock is to be usable in the dark.

Binary-coded sexagesimal clocks

Binary clocks that display time in binary-coded sexagesimal also exist. Instead of representing each digit of traditional sexagesimal time with one binary number, each component of traditional sexagesimal time is represented with one binary number, that is, using up to 6 bits instead of only 4. For 24-hour binary-coded sexagesimal clocks, there are 11 or 17 LED lights to show the time. There are 5 LEDs to show the hours, there are 6 LEDs to show the minutes, and there are 6 LEDs to show the seconds (which aren't used in clocks with 11 LED lights). Binary clock Swiss railway station

A format exists also where hours, minutes and seconds are shown on three lines instead of columns as binary numbers.

Binary time

Less commonly, the day could be divided in binary fractions, such as ½ day, ¼ day, etc. The clock would show the time in 16 bits, where the smallest unit would be exactly day, or (about 1.318) seconds. An analog format also exists of this type. However, it is much easier to write and express this in hexadecimal, which would be hexadecimal time.

References

{{Reflist Clock designs Time measurement systems Binary arithmetic