Sunday 19 June 2016

Rotor Clock

There seems to be a bit of fad for clocks that spell out the time. There are even some online examples utilising a variety of languages. And jolly good they are too!

Spelling out the time in British English is fairly simple. Just take the local time and extract the minutes. If the value is less than thirty, express the time as

  (minutes) PAST (hour)

Otherwise, use

  (60-minutes) TO (hour+1)

There are some exceptional cases; if the minute value is zero, use

  (hour) O'CLOCK

Whereas minute values or 15, 30 and 45 are generally expressed as

  HALF PAST (hour)
  QUARTER TO (hour+1)

It turns out that, using the above scheme, the maximum number of characters needed to spell out the time is 32. For example:


If we are a little bit lenient with the spacing between the words, we can prune the number of distinct characters in each position to ten (including space). This leads to an interesting configuration for a mechanical device that can spell out the time using 32 rotors of only 10 facets each.
With a little bit of CSS3 and HTML5, it's possible to produce a web page that brings such a device to life. If you further optimise the HTML, CSS and Javascript, you can present it in a single file of only 2191 bytes.

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