Title text: The month names are the same, except that the fourth month only has the name 'April' in even-numbered years, and is otherwise unnamed.
This comic pokes fun of attempts to "fix" the calendar by making it simpler or more rational, which inevitably result in a system just as complicated. This is an example of the paradox in complexity theory that if you attempt to simplify a system of problems by creating a new system of evaluation for the problems you often have instead made the problem more complex than it was originally.
 Length of Year
Because there are approximately 365.2422 days in a solar year, various calendars use different means to keep the calendar year in sync with the solar year and the seasons. The Julian Calendar, for example, has leap days every four years, giving it an average day length of 365.25 years. The most widely used system is the Gregorian Calendar, which also has leap days every four years, but skips leap days in years divisible by 100 unless the year is also divisible by 400. This gives it an average day length of 365.2425 days, which is very close to the length of a solar year.
Other calendars have been proposed, such not counting leap days and special "festival days" as a day of the week, in order to make every date fall on the same day of the week every year.
Randall advertises his idea for an "Universal Calendar for a Universal Planet". He combines calendar definitions with time zone definitions. The abbreviation EST is a joke on the American Eastern Standard Time.
- At "24 hours 4 minutes", EST days are longer, though there are only 360 of them in the year. The extra 4 minutes over the course of 360 days adds up to one standard day, so Randall's EST calendar would at this point have a year that is 361 standard days long.
- Running the clock backwards for 4 hours after every full moon gives 8 additional hours at each full moon, twelve or thirteen times in a year. Because a thirteenth full moon will occur once every 2.7 solar years on average, this modification adds 4.1228 standard days to an EST year, bringing it to 365.1228 days.
- The doubling of the non-prime numbers of the first non-reversed hour after each solstice and equinox is a final, very complicated way to bring Randall's EST year in extremely close sync with the solar year. There are 17 prime numbers between 0 and 59 and 43 non-primes. There are 2 equinoxes and 2 solstices each year, so a total of 172 minutes will occur twice. This brings the average length of Randall's EST year to 365.2422 standard days, equal to the solar year to four decimal places.
 Claimed Benefits
Many of the claimed benefits for the calendar are highly dubious:
- While it is fairly simple to describe, EST is far from simple to understand or put in practice. Clocks in particular would have to regularly undertake very complicated processes like running backwards or duplicating non-prime minutes.
- EST does appear to be fairly clearly defined.
- EST fails completely to be unambiguous. Following each full moon, four hours occur three times, twice forward and once backward. Several minutes are also duplicated, making times during those periods ambiguous.
- The only way EST is free of historical baggage is that it breaks free of any sensible bits of historical baggage; it keeps such things as the 30-day month and 12-month year, but adopts a different (and variable) length of day that would make it wildly out of sync with the Earth's day-night cycle.
- EST is compatible with old units, as far as seconds, minutes, and hours are concerned, though not for days, months, or years.
- EST is indeed very precisely synced with the solar cycle.
- EST is free of leap years, though some EST years are 8 hours longer than others on account of having an extra full moon.
- A calendar amenable to date math makes it easy to find the length of time between two dates and times by having standardized periods of time. The complex variability of the length of EST years, days, and hours mean it is only intermittently amenable to date math, which is to say not at all.
 Other Features
The features of the calendar get increasingly bizarre as the description proceeds:
- The Epoch for EST is set by reference to the Julian calendar, which was superseded by the Gregorian calendar. The Julian calendar is currently 13 days behind the Gregorian calendar.
- The different zone for the United Kingdom is a reference to 1 yard being equal to 0.9144 meters, a pun on using imperial units instead of the metric system.
- Randall does not like Daylight Savings Time very much, as mentioned later in 1268: Alternate Universe.
- Narnian time is a reference to the fictitious world of Narnia in CS Lewis's The Lion, The Witch and The Wardrobe and its sequels. In Narnia, time passes much more quickly than in the real world. You could be in Narnia for several days and only a few minutes would have passed in the real world. However, synchronizing this effect would be impossible because it is not a consistent rate; it fluctuates wildly based on the whims of drama and magic.
- The Gregorian calendar does not include the year "0", after "1" BC the next year is "1" AD. Randall's invention fixes this according to correct Mathematics, only to reintroduce the problem immediately by arbitrarily omitting the year 1958. The year 1958 is significant because January 1, 1958 is the epoch (time zero) in International Atomic Time (TAI), which is part of the basis for Coordinated Universal Time (UTC). (The main difference is that TAI doesn’t add leap seconds).
- The title text may be a reference to the ancient (Pre-Babylonian Exile) Jewish Calendar, which did not name the months, rather assigning them numbers from 1 to 12. The names used by Jews today are the names of the Babylonian months, derived from various Babylonian deities.
- XKCD[sic] Presents
- EARTH STANDARD TIME
- A Universal Calendar for a Universal Planet
- EST is...
- Simple * Clearly Defined * Unambiguous
- Free of Historical Baggage * Compatible with Old Units
- Precisely Synced with the Solar Cycle * Free of Leap Years
- Intermittently Amenable to Date Math
- Second: 1 S.I. Second
- Minute: 60 seconds
- Hour: 60 minutes
- Day: 1444 minutes (24 hours 4 minutes)
- Month: 30 Days
- Year: 12 months
- For 4 hours after every full moon, run clocks backward.
- The non-prime-numbered minutes of the first full non-reversed hour after a solstice or equinox happen twice.
- 00:00:00 EST, January 1, 1970 = 00:00:00 GMT, January 1, 1970 (Julian calendar)
- [Time Zones]
- The two EST time zones are
- EST and EST (United Kingdom). These are the same except that the UK second is 0.9144 standard seconds.
- Daylight saving: Countries may enter DST, but no time may pass there.
- Narnian Time: Synchronized.
- Year Zero: EST does have a year 0. (However, there is no 1958.)