A binary-coded decimal clock uses one column per digit of the time — two for the hours, two for the minutes, two for the seconds. In each column the dots stand for 8, 4, 2 and 1 from top to bottom; add up the lit ones and you have the digit. So a column with the 4 and 1 lit means 5.
Some columns need fewer dots: the tens of hours go only up to 2 and the tens of minutes and seconds only to 5, so the unused rows are drawn small and dark. In stopwatch and countdown modes the columns show minutes, seconds and hundredths instead.
Where it's useful
- Learning how binary works with a clock you can check against the real time
- A nerdy desk clock or a talking point on a stream
- A puzzle for a classroom or coding club
- A distinctive countdown for a tech event
Three ways to use it
- Clock — the time of day in your time zone or any city, in 12- or 24-hour form.
- Stopwatch — counts up with laps; press Lap while it runs.
- Countdown — counts down from any time you set, sounds at zero, then counts overtime.
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Questions
How do I read a binary clock?
Each column is one digit. Add the values of the lit dots — 8, 4, 2 and 1 from the top — to get that digit. Read the columns left to right: hours, minutes, seconds.
Why do some columns have fewer rows?
The first digit of the hours only goes to 2 and the first digit of minutes and seconds only to 5, so they need fewer binary places.
Does it show the decimal digits?
Yes, under each column, so you can learn by checking your reading.