Last updated: 2019-10-01

Most documents, especially those with some legal significance or those that are revised routinely, carry dates. In the amateur radio context, dates are clearly very important for reporting propagation events or even for confirming individual contacts by way of QSLs.

There are easy and unambiguous ways to write dates. The simplest is probably just writing out the name of the month. This technique works, but has two drawbacks. Firstly, it is cumbersome as the names of some months (e.g. September) require a lot of space on what might sometimes be cramped documents. Secondly, the format is only unambiguous if you happen to speak the language it's written in. While some may feel that a specific language is universally known (this attitude is often found among Mericun speakers), it is not in fact the case.

We might thus conclude, very reasonably, that some form of numerical format is required. Numerical formats have a fixed length, something that is very useful if one is trying to squeeze a date into a confined space on a QSL card. They are also universally comprehensible to anyone using the same calendar and the same number system. While neither of these requirements is trivial, they do cover the vast majority of the earth's population. That's about as good as we can hope for.

Unfortunately, a number of numerical date formats have proliferated. Probably the most universally known and used format is 01/02/03. The only problem is that this notation could mean any of a number of things, depending on who is reading it. If a Mericun reads it, it probably means "January 2, 2003". If a European reads it, it will probably turn out as "1 February 2003". The odd free thinker may even interpret it as "3 February 2001". The Y2K problem has already highlighted the importance of four digit years, but unfortunately the year 2000 itself can be abbreviated as "00". Many feel that this abbreviation is unambiguous, and have continued to merrily use their old formats.

Another attempt at making dates less ambiguous is the habit of using Roman numerals for the month. This technique resolves the ambiguity w.r.t. the Mericun notation, but is of variable length and cannot easily be sorted.

Fortunately, there is a standard that was set in the Sixties, and that is supposed to be an international standard without ambiguity. Apart from this advantage, it also lends itself to simple sorting, and is fully consistent with our other number notations.

The ISO 8601 format is YYYY-MM-DD. Today's date, as this piece is being written, is 2000-12-07. The use of hyphens rather than slashes distinguishes this format from its older cousins, ensuring that there is no ambiguity, even when the abbreviated format of YY-MM-DD is being used. ISO 8601 is also the standard in South Africa (SANS 8601) and most other countries.

The other advantage, already mentioned, is that such dates conform with our number notation and can be alphabetically sorted. When we learn to write, we're told repeatedly that the most significant digits are written on the left, and the least significant ones on the right. Clearly, in a date the year is most significant, while the day is least significant.

The advantage becomes even more apparent when the time is also specified. Let's take an example, where we have to sort several events in chronological order. The three events are:

In this format, these events can be sorted in ASCII or numerical order. They will come out in the correct order, even though they are not specified to the same level of precision. If a programmer decides to omit the dashes and/or colons from a database, the sort order is completely unaffected.

If the dates were written in some other format, they would certainly not emerge in the correct sequence, unless some pretty nifty sorting algorithms were employed.

When I first wrote this piece, the new milennium had just broken, and I wondered whether those habits would change. Almost two decades later, I'm afraid the answer is mostly "no". However, in the context of amateur radio, there are several promising signs. All major log formats (including Cabrillo and ADIF) use ISO dates. Also, several major systems used by radio amateurs use the format. The ARRL's Logbook of the World and G7VJR's ClubLog both use standard date and time formats. Hopefully, the exposure will influence users into adopting the standard format. Given the large number of users that these systems have, the influence is likely to be positive.

Practical suggestions

Always write the date YYYY-MM-DD, or if you really have to abbreviate, YY-MM-DD. Always use hyphens as separators; using slashes introduces ambiguity. If you want to list several dates within a single year, ISO 8601 recommends using two dashes before the month (i.e. "--04-25").

Always write the time with colon separators: HH:MM:SS,S or HH:MM.

If you're writing both date and time, use the format YYYY-MM-DD HH:MM:SS.

If you're recording multiple dates and times, keep the columns aligned even if you're not recording all the information for each record. The example above, once sorted, becomes:

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