An Essay on the 24 Hour Watch
The 24 hour watch dial, known and used historically in aviation circles, is lesser known to those who use a 12 hour watch or clock to tell time every day. I recently learned about the existence of 24 hour watches. Now that I have been exposed, I have doubts that I can ever go back to telling time with an instrument that must hit each number on the dial twice during a “day”. Or at the least, I’m not sure if I want to. For me, the 24 hour watch is a thing of simple beauty; the problem is I have spent 53 years telling time using the ingrained memory of a 12 hour dial. There are new things to learn.
This essay will only consider the true 24 hour watch on which the hour hand moves one full revolution in a twenty-four hour day. By definition, a 24 hour dial has more information to convey, and can appear more cluttered, than a 12 hour dial. There are twice as many hour indexes to squeeze into the same space. This necessitates them being placed much closer together and puts hour indexes in locations on the dial where we are not used to seeing them. This requires careful design by watchmakers, and applied knowledge by the watch user, to be able to tell the time proficiently. “Proficiently” may sound like a strange word to use to describe telling time, but the 24 hour dial requires the user to acquire new knowledge of the landmarks or reference points that define time on the dial to use it without having to work at it.
The most important reference point on a 24 hour watch is “the top”, or what we normally refer to as 12 o’clock on a 12 hour dial. On a 24 hour dial, the top is typically denoted with the 24 or 12; the 24 referring to midnight and the 12 referring to noon. Some watches may use 00 in place of the 24. We could have a whole discussion about “24 is really 0000”, but we can argue that on a different day. For now, I will use 0000 to say the time at midnight, and 0001 for a minute past, but 24 is the index on the watch.
Here are two styles of 24 hour dials; a 24 on top (blue), and a 12 on top (black); both photos from the Glycine web site:
The number “at the top” describes the style of the 24 hour watch, so I’ll refer to it as the base index, 12 or 24.Both styles have 0600 and 1800 at what we know as the 9:00 or 3:00 on a 12 hour dial. I’ll refer to the 9:00 o’clock position as the “left side index” and the 3:00 o’clock position as the “right side index”. Eventually, we need to get away from references based on our knowledge of the positions on a 12 hour dial and see the watch in a whole new way. We’re not there yet, though.
It helps to visualize the dial in two halves, a top and a bottom. On a watch with 12 on top, also known as a purist, the left side index starts the sequence of times at 0600 and the right side index ends it at 1800. Advancing clockwise from the left side index are 0700, 0800, 0900 ………. on to 1200 at the top, then to 1300, 1400, 1500…… and ending up on the right side index at 1800. 0600 and 1800 are the 24 hour equivalents of each other; 6 a.m. on the left and 6 p.m. on the right. I’ll refer to them as the “companion times” of each other. Companion times are always twelve hours apart and directly opposite of each other on the watch dial.
Continuing clockwise past 1800, each hour index is a companion time of its counterpart from the top half of the dial. For example, 1900 is the companion time of 0700, 2000 is the companion time of 0800 ………. 0500 is the companion time of 1700, and finally back to 0600. All twenty-four hours are denoted once, and the hour hand only hits each index once, in a single revolution of the watch dial. This is the key feature of telling time this way.
If you can visualize this concept, you will see that on a watch with 12 on top, the top half of the dial is comprised of “daylight hours” and the bottom half of “nighttime hours”. This is actually an intuitive part of the 24 hour dial. Day over night; top over bottom, half and half. With a 24 at top watch, the night is over day, but the concept is the same. Some watches, like the blue Glycine above, use a darker color on the dial half for nighttime, or divide the bezel into two colors which can be used to denote day and night hours. Some prefer this design, but it is not required once the concept is understood.
Study the graphic of a 12 on top dial below and note the positions of hour indexes that are in locations that are not familiar to us. Notice that 0600 and 1800 are nowhere near where we expect to find 6:00 o’clock on a 12 hour dial. In fact, there are only three indexes that will be anywhere near where we have learned that they should normally be. These are the base index on top and the two indexes on either side of it. The “on top” is exactly where it is expected and the other two are close, but slightly off. In this case, 1100 and 1300 are near where they are expected, but a little closer to 1200 than normal. The indexes are squeezed closer together so that 13 numbers fit in the top half of the dial. Without utilizing this knowledge, it would be easy to misread 2000 as 4:00 o’clock.
12 hour dials are frequently referred to as being more “intuitive” but nothing could be further from the truth. We learn the hour index positions as children and they become ingrained in memory until we can tell time on a 12 hour dial that doesn’t even have any indexes. There are four primary indexes on a 12 hour dial; 12:00, 3:00, 6:00 and 9:00. These indexes are “straight up and down” or “straight side to side” on the dial. I’ll call them “up and downs”. Between each pair of up and downs are two other hour indexes. For example, between 12:00 and 3:00 are the indexes for 1:00 and 2:00. Between 3:00 and 6:00 are the indexes 4:00 and 5:00, and …. and on around the dial.
It is easy to recognize when the hour hand falls on an up and down index or on one of the in-between indexes. This is not intuition, but merely rote memorization of the points and familiarity with the location of the hands relative to these positions. The same thing goes with the minute hand. The distance between each index, is 5 minutes. At a glance, we can tell the time on a watch that has bold lines for the hour indexes and finer lines for minutes in-between the hour indexes. We don’t even need numbers because we have learned all the positions. We need to apply this concept to the 24 hour dial to tell time “intuitively” based on the positions of the hands relative to a larger number of reference points.
Use the graphic of the 12 on top dial for this next section. Break the dial down into four quadrants with the reference points of 0600, 1200, 1800, and 0000. In between 0600 and 1200 there are two even hour indexes; 0800 and 1000. All four are even hours, and if they are all marked the same, it is relatively easy to identify 0600, 0800, 1000, and 1200. There are three odd hour indexes in-between the even indexes; 0700, 0900, and 1100. If they are marked with a different shaped index, say a round dot, they are also easy to tell. If the hour hand is in-between 0600 and 0800, then the dot it’s on is 0700. If the hour hand is in-between 1000 and 1200, then the dot it’s on is 1100. The concept is the same as with a 12 hour dial, the difference is that there is twice the number of indexes to deal with. There is also a relationship between the hour and minute hands that needs to be recognized to determine when it’s coming up to an hour or has gone past the hour. This is the same when using a 12 hour dial and we are all familiar with the concept.
Watches, like the Glycine Airman, that use lines for the even indexes and dots for the odd indexes help facilitate time reading without visible numbers. The Glycine has small numbers, but they are not always visible. This should not inhibit the ability to tell the time “proficiently”. Some Airman models don’t have an index for the odd hours, just the number. Watches like the Aviator 24 Hour that use large numbers for every even index and unmarked lines for the odd indexes accomplish the same thing in a different way. The Aviator may be easier for the new 24 hour dial user because the lumed numbers are visible even in the dark.
Some designers get creative and use different index patterns that may omit one or more key reference points in a section of the dial. This can make it difficult for the new user of a 24 hour watch. Omitting one index, like the 1800 on my Glycine, where the date window is does not cause much of an issue. This is especially true since it occurs at a main index that is easy to identify, one of the “up and downs”.
Examples of some other 24 hour dials (from russia2all.com):
This has been a very basic attempt to pass on what I have learned in the past three days since acquiring my first 24 hour watch. It has given me a new found interest in the delineation of time and I am having fun with it. There are watches that have 24 hour dials with regular 12 hour hands and a single 24 GMT hour hand. Those are a whole different topic for discussion and beyond the scope of this essay. Thanks for reading.