3 Minute Marks on Pilot’s Chronographs: (Partially) Debunking Myths and (Some) Dead Reckoning

Yes sorry, I accidentally mixed definitions by using the word “independent” when I only meant “a fourth hand, that is a second hour hand” (as opposed to the later invention of an independently-setting hour hand).

So yes, early 50’s, 1952, should be the earliest this trailing/secondary 24hr hand was around, but I don’t know of many models that early that don’t rhyme with “polex” 😎

Glycine.

With a secondary GMT hand? 👎

😗



👍

In this post, below, I’ll include pics from the 1951 booklet, printed in Switzerland, by the “Swiss Federation of Watch Manufacturers” - but only those pages relevant to the “mere 3/6/9 emphasis” marks.

In a separate thread, I’ll post the entire booklet, as it’s a rather interesting little piece of history (and when I’ve done some I’ll come place a link here to that separate thread).

It also raises a few interesting questions about the relationship of this booklet to the watchmaker’s book, first published in 1956, and earlier discussed here and here.

Knowing now for certain that this Swiss Federation booklet predates the watchmaker’s book by several years, it would appear the latter watchmaker received permission (or didn’t) to essentially copy the watch plate diagrams and repackage the descriptions for the similar chapter in his book.

Accordingly, this 1951 booklet is so far and in effect the sole primary resource stating that the “mere 3/6/9 emphasis” marks were for timing telephone calls. (The watchmaker’s book reference being only a regurgitation of this booklet’s materials.)

The booklet is a rather persuasive and authoritative primary source support for the phone call hypothesis regarding the “mere 3/6/9 emphasis” marks. It does not help us with the nuances around the apparently limited applicability of these marks to different markets that did not follow the (let’s call it for now) European convention for timing long distance calls. Nor does it help us with the (I believe) separate matter of the more concerted pilot’s watch features emphasizing 3 minute increments more broadly. But it does give us a single authoritative primary source assertion from an organization that, while not a manufacturer asserting it’s own rational for the design of a specific watch, is still presumably knowledgeable.

For completeness, and I had to look this up: the “Swiss Federation of Watch Manufacturers” was a predecessor entity to the more familiar FSWI: “The Federation of the Swiss Watch Industry was established on 19 November 1982 as the result of the merger of the Swiss Federation of Watch Manufacturers’ Associations (founded in 1876) and the Swiss Chamber of Watchmaking (founded in 1924).”

Before the 1980 merger, the Federation was basically a industry lobbying organization, representing the sector as a whole, both in Switzerland and abroad, facing the media and the public in general, coordinating policy-making within the industry, etc.

It would do things like take out ads to encourage people to buy watches:






The Federation even commissioned Norman Rockwell to create a piece that was used in its campaigns of the period (the original of which doing rather well at auction a few years back):









While I’d much rather have a dozen period explanations from manufacturers describing the intended utility of specific watches they designed and marketed, this assertion instead by the Federation is a next-best thing for present purposes.


It does, though, leave me still baffled by the number of period catalogues I’ve gone though that say nothing about this design feature, despite saying almost everything else imaginable. While some have chimed in to say, “well maybe it was so obvious,” I can only be forced to begrudgingly accept that for now, despite the fact these brochures and catalogues didn’t mind saying any number of more obvious things (eg, that a 30 minute totalizer counts the number of minutes up to 30, etc.).

What’s more: this booklet itself is a perfect counter-example to the “it was so obvious” - issued in 1951 when it seems chronographs were catching on more broadly, it does in the very first example appearing in the booklet, describe the function quite clearly and prominently (which makes sense, given that almost every other chronograph featured in the remaining book features these marks).

All that background and support for the authority laid out, here are the relevant pages from the Federation’s 1951 booklet:

The entire booklet can now be found here

Well, you were correct about the description, but it for me only raises now another mystery:





This booklet was printed in 1951. This page clearly describes a secondary “small red indicator hand E’ bearing the letter “N”” and further that this secondary hand “completes one turn of the dial in 24 hours” and is adjusted by means of crown ‘O’.

Now, 1951 is before even the Turn-o-graph much less the first GMT Master. I thought the latter was the first watch to add such a fourth hand keyed to 24hrs (eg 1 rotation of dial per 24hr) in addition to the main 12hr hand? (Distinguishing this from the Glycine Airman, which was simply a 24hr movement adding a rotating 24hr bezel).

Am I mid-remembering my purported watch history here, or does this 1951 booklet purport to show some unknown model that predates the GMT-Master’s four hand setup (even if put to a different use)?

sure did, apparently as early as 1943:

https://omegaforums.net/threads/195...-booklet-on-chronographs.138683/#post-1887090



http://www.galletworld.com/gallet_watch_multichron_navigator.html

The beauty of birdwalks such as hunting down the watch above, is that it uncovered some accidental-additional information relevant to this thread:

First, it appears the Federation also created a version of this booklet for the Italian market (I only found this page so cannot be certain it is from the Federation, but the reason for my inference should be clear):




So, I believe we now know of an English, French, and Italian version of this marketing/educational booklet.

The birdwalk also stumbled onto an alternate English version:





In this alternate version of the booklet (like in the Italian version), aside from the differing layout and quality of drawing, it includes on the dial the brand


So it would appear the Federation (presumably) made multiple versions of this booklet, in multiple languages, all reiterating the telephone assertion.

The missing link: Pilot’s are notorious for calling their mums

Having spent a good bit of timing chasing the “mere 3/6/9 emphasis” relationship to long distance calling charges in Europe, and having found at least one primary source reference to this rationale …

Later, I’ll come back around to turn back to the separate utility of chronographs to dead reckoning and similar types of maritime and aeronautical navigation, a utility of which there is little serious doubt… (a 1967 advertisement from Flying magazine that is preview for this particular Omega-centric audience):

Thought I’d add the version geared toward maritime navigation as well:

Great research. Keep up the good work! 😀
Looks like Zenith had the makings of a GMT pilots watch but didn't know it yet. Had they taken the simple step of putting a rotating bezel on it and marketing it as a watch for airline pilots when air travel started to take off (pun intended), it might have been this watch rather than the Rolex GMT Master becoming the icon it is today.

Following on the last two 1960’s Omega adds (run repetitively in various boating and flying magazines from ~1966-1969), and to try and clear some fundamental underbrush of skepticism:

Early in the thread, there was expressed some skepticism around the utility whatsoever of a wrist chronograph to flying.


I’m the last one who should squint at skepticism, so as a preliminary matter I thought I would more thoroughly address this question regarding the general utility of chronographs to flying.

While my original post contained a link to a navigational instruction document that revered the chronograph as the second most important instrument in a cockpit after the compass, that document was relatively contemporary and was perhaps viewed as lacking period authority.


Below is an article from Flying magazine, 1946, titled “Time and the Airman.” It covers broadly the utilization of chronographs and stopwatches to the airman, from on-board to the wrist.

Relatedly, also earlier in this post there was expressed some skepticism about the utility of a wrist chronograph, when — I think the criticism goes — there would be various sorts of on-board instrumentation to perform navigational calculations.


My original post also had content addressing this sub-point. But to briefly address this sub-topic of continued skepticism, I also include below a few additional period excerpts. Those excerpts, in short, show that variously pilots utilized their wrist chronographs as either primary or secondary navigational timers when, e.g., they had simple aircraft, or their aircraft mechanicals were malfunctioning, or they had occasion to disbelieve their aircraft mechanicals and utilized their wrist chronographs to perform confirmatory calculations and regain trust in their on-boards. (Moreover, while not addressed in my excerpts below, elsewhere there are discussions of pilots who were switching between aircrafts, they themselves did not maintain or know to have reliable instruments, preferring to have at least their own wrist watch with a “rate known” and personally-maintained certainty of accurate timekeeping.)

I should mention that there are exhaustive historical materials that either directly or by inference make it absolutely undeniable that both on-board and wrist worn chronographs were (and continue to be) indispensable to pilots. To a degree, having to “prove up” this point feels a bit like describing the color blue - almost so fundamental as to become difficult to know best how to “explain.”

Accordingly, the few excerpts below (together with those from other posts to date), I found to be merely exemplary in their content, period, and - importantly - still yet good reads for anyone not needing convincing.

Collectively the materials to date addressing whether chronographs, including wrist chronographs, were useful to pilots should put that separate discussion to bed enough for present purposes. That way, later, we can move past that assumption and zoom into the lower level questions about how certain watch designs may or may not have aided (or been marketed to aid) such pilot’s needs.

Up first is the 1946 long form article specifically addressing the broad relationship of pilots to their clocks, with a bonus topical Universal Geneve add on the last page (marketing its utility to pilots).







Next up is a 1955 article that is focused on the utilization of certain flying techniques to achieve altitudes and speeds and low fuel burn rates; the author was so surprised by the success of his methods to achieve speed, as told by his more sophisticated instrument panels, he goes to his chronograph to (in effect) manually check his ground speed and is pleased to find both methods agree.

(Note also that this is an instance of a pilot using the rule of 3/6 as a method to determine ground speed despite the existence of an on-board speedometer and equipment that accounts for ground speed - so the equation of [distance = speed X time] can be manipulated to solve for either ground distance or ground speed, depending on the pilot’s needs.)




Next up is an article from 1951, wherein the author is essentially arguing that even the compass is so unreliable (or unwieldy) in certain situations that only the chronograph (a mere “$2 tool”!) is the reliable pilot’s tool.

(Note in this article only the recognition that most pilots of small craft, hobby, etc., are performing rough calculations constantly from their chronograph, essentially in short hand, as their baseline certainty for navigation.)





By the way, on the separate but related topic of whether manufacturers were marketing these utilities to pilots, the dozens (hundreds?) of period materials I’ve been through are saturated with evidence. For fun, below, I’m including just a few such example ads from the magazine editions excerpted above (aside from the UG add embedded above)

@cvalue13
Thanks once again for all your research into this topic. Re your post above:

As a formerly active recreational pilot flying light aircraft, I can attest to the importance of an accurate and reliable timekeeper when navigating. It's main use was for recording times on arrival at waypoints and when nav fixes were taken. It was also for keeping track of elapsed time and subsequently calculating things such as fuel remaining, ground speed, revised ETAs etc. Whilst a chronograph would have been desirable, it was not absolutely essential. In fact, this was my "pilots watch" back in the day (over 20 years ago):


Most of my flights were of short duration and used Visual Flight Rules (VFR) where determining your location was done by taking fixes using features on the ground as references. I have kept some of my old in-flight worksheets and I have included one here to give you an insight into what a pilot keeps track of in flight. It was one of my earliest navigation exercises:


This sheet was attached to a clipboard, which sat on my lap as I piloted the aircraft. Each flight was divided into "legs", with the first leg in this case from position MB to YIVE. Abbreviations and their meanings:
PSN: Position
LSA: Lowest Safe Altitude (in hundreds of feet)
FL or ALT: Flight Level or Altitude (in hundreds of feet)
TAS: True air speed (in knots)
TR(M): Track (Magnetic). This is your direction of travel over the ground.
WIND: Forecasted direction the wind is coming from and its strength in knots.
H/M: Magnetic heading. This is the direction the nose of your plane is pointing. This is what concerns me most when I fly, hence the asterisk for quick reference.
G/S: Ground Speed. This is an estimate, based on the TAS, intended track and wind.
DIST: Distance in nautical miles.
ETI: Estimated time interval for that leg (in minutes)
PLN EST: Planned estimated time of arrival at that waypoint based on forecasted wind and ground speed. The numbers here represent the minutes of the hour.
REV EST: Revised estimated time of arrival at a waypoint based on ACTUAL ground speed. Recorded as minutes of the hour.
ATD ATA: Actual time of departure/arrival at a waypoint. Recorded as minutes of the hour.

Times were recorded in UTC (Universal Coordinated Time, formerly GMT). In this case, my planned departure time was 0400Z but actual departure time was recorded as 0421Z. For the first leg, the ETI was 34 minutes, with an estimated arrival time of 0421Z+34 minutes at the first waypoint. This gives 0455Z. However, my revised estimate was 0447Z because of weaker than expected headwinds. The revised estimate was calculated at the halfway point of the leg. The most accurate way to work it out is by firstly calculating actual ground speed by dividing distance covered by elapsed time and then using this info to work out how much time it would take to cover the remainder of the leg. This can be done using either a circular slide rule or electronic calculator. Mostly though, we just used a rough rule of thumb. For example, if I arrived at the midpoint of the leg 2 minutes ahead of schedule, then I can expect to arrive at the end of the leg 2x2=4 minutes ahead of schedule. In this particular instance, I would have been 4 minutes ahead of schedule at the midpoint of the first leg, given that my revised ETA was recorded as 8 minutes ahead of schedule. My actual arrival time at the waypoint though was 0449Z.

Nav fixes and the times they were taken were recorded in pencil on a map. We were advised to take a fix at least every 20 minutes or so. Course corrections, if needed, were usually done at the midpoint of the leg as well.

With regards to the 3/6/9 minute time intervals on some of the chronographs that you posted, I can't say that they would have been of much use to me personally for the type of flying I was doing. The "6 minute" rule could have some applicability for working out distance covered in instrument flying and "dead reckoning" but that's all I can think of. In any case, some of the literature you've uncovered has shown that these intervals were more for timing long distance phone calls back in the day. And given pilots were often a long way from home, this would make sense.

As a rec pilot flying light aircraft, a Breitling Navitimer with its rotating slide rule for calculations would have been more useful to me than 3/6/9 minute markers on the chronograph. It would be less cumbersome than pulling out the full size nav computer from my flight bag in a cramped cockpit:


And 24 hour timekeeping watches such as the Glycine Airman and Rolex GMT would only have been useful to those pilots doing long distance flights crossing multiple timezones.

Anyway, apologies if this post is a bit long winded but I hope it helps people understand what a pilot might find useful in a watch.

Thank you for all the information! Zero reason to apologize, least of all for being long-winded (who am I to judge 😁).


It’s interesting to me that you say this, because as I was reading your very good explanation of your process…


… you sounded just like the quote from the navigation primer linked in my OP:

QUOTE="cvalue13, post: 1880966, member: 4265"]As put by a different navigation white paper (in the maritime context), “The six-minute rule … sounds almost too simple to bother with until faced with trying to calculate the distance traveled in five minutes (how many of us can quickly calculate one-twelfth of eight nautical miles?)…It is much easier to lay down a DR track at 6-minute intervals (or a multiple of 6, since the rule can be used easily for 12-, 18- or even three-minute intervals) than to struggle to find the calculator or the circular slide rule..[/QUOTE]

In fact, back to your example “rule of thumb”: in it, you’re describing a need to “work out how much time it would take to cover the remainder of the leg.” In your example, you’re at the midway point of a leg, so your rule of thumb outlined (just double your halfway time delta) works very well, even in the minds of the mathematically dense (like myself).

But in other situations, not midway of a leg, isn’t the 6-minute rule just another “rule of thumb” that can be used to “work out how much time it would take to cover the remainder of the leg”?

Like in your example, assume you know the ground distance just covered at a given checkpoint on the leg, and also your elapsed time to that checkpoint: let’s say it’s 28 nautical miles of ground covered in 13 timed minutes. Let’s also say your next checkpoint is in 40NM, and so now, your problem goes, you want to estimate how much time it will take to cover that 40NM.

If you’ve just gone 28NM in 13 minutes, and have 40NM to go, then using the “6-minute rule” you can easily and quickly deduce and estimate all of the following:

-> your ground speed has been ~130 nautical miles per hour (because your ground speed has been ~13NM/6 min., and 6 is 1/10th an hour)

-> if maintaining the same air speed (and wind, etc.) you’ll continue to travel ~13NM/6 min. (Or, just the same, ~6.5NM/3 min., ~19.5NM/9 min., ~31.5NM/15 min., etc.)

-> so, you will arrive at a checkpoint that is 40NM in just over 18 minutes (~13mi/6min X 3 = ~39mi/18min), you’ll be halfway there in 9 minutes, etc.

This is really all there is to the “6-minute rule” (or the rule of 3 or 9 or 15 etc.).” Similar to your “rule of thumb” used to avoid reaching for the slide rule, so too is the “6-minute rule” purportedly just another such tool.

(All this is of course aside from the separate topic of whether specific features of pilot’s watches were useful to navigators. In your response, it seems I’ve still not been clear: I, too, am most certain that the “mere 3/6/9” marks found on many chronographs (including many non-pilot chronographs) were more likely for timing European long distance calls (though for completeness I’d like to find more primary information); but as a separate matter, I view as still up for debate the reasons for other types of design changes in certain pilot’s watches that go to great lengths to emphasize intervals of three minutes in the chronograph (i.e., not the “mere 3/6/9 emphasis marks on otherwise normal chronographs, but instead those watches marketed to pilots and for which manufactures went to some greater lengths to make prominent intervals of 3 minutes, e.g.,:




For this design Breguet (1) increased the size of the minute totalizer, (2) changed the underlying movement to display a maximum of not 30 but instead 15 minutes, (3) placed the totalizer’s indices not at the 5 but instead 3 minute intervals, and (4) made these indices and the totalizer hand luminous. I was think it more likely Breguet did all this for purely aesthetic reasons than think Breguet did all this to time phone calls (none of these changes are needed, afterall, to time a phone call - the usual dial marks would have been sufficient.)

While somewhat on the topic still of aeronautical navigation, this post explores the embedded idea that such navigation trades in short time frame intervals (i.e., less than 15 minutes).

From over here at “Aero Antique - preserving war bird history one artifact at a time” is an example of a “jitterbug” navigator’s stopwatch made specifically for determining ground speed.




I’ll except the relevant bits of the description (my emphasis in bold):

“Here is an authentic WWII-era aircraft navigator's Watch, Navigation (Ground Speed) Stopwatch, Type A-8, made by Elgin to Air Corps US Army spec #94-27749. With a serial # AC42-670, indicating manufacturing year of 1942. Type A-8 stopwatches were used in any WWII aircraft with a navigator, such as heavy (B-17, B-24, B-29) and medium bombers (B-25, B-26) and large transports (C-46, C-47, C-54).

The outer ring of the dial counts up to 10 seconds and the inner dial located at the standard 12:00 position count up to 10 minutes of the 10-second revolutions. The A-8 was known as the ‘jitterbug’ because of the loud and fast ticking of the balance at 144,000 beats per hour. Yep, just try to hear that over the cacophony of multiple radial engines...

According to C.G. Sweeting’s book "Combat Flying Equipment":

The Type A-8 was a navigation stopwatch designed for timing ground speed meters for determining the velocity of aircraft relative to the ground. One revolution of the Type A-8 hand was equivalent to ten seconds….

After winding, one press of the crown starts the second hand in motion. As the hand passes 10 seconds, the small hand on the inner dial advances one mark on the scale and counts minutes. One revolution of the inner hand is 5 minutes, another revolution is 10 minutes. Another press of the crown stops the hands.”

As these ground speed jitterbugs were one of the most mass produced issued watches, a quick look around the internet finds many of these for sale, all with this military spec’s dial arrangement, together even with some cool “box and papers”




It’s notable that the navigators in these heavy aircraft were issued “jitterbugs” that could time no more than a 10 minute interval, max.

It’s notable, I think, because it suggests that for some aeronautical navigation techniques viewed as critical (if not critical, why issue all navigators these spec’d stopwatches fit for purpose?), navigators were trading in time increments generally less than 10 minutes (otherwise, why not have a minute totalizer up to 15, 30, or 45 minutes?).

If you’d like to listen to the “jitterbug” buzzing at 40 beats per second (!! four times as fast as Zenith’s high-beat El Primero),, here’s a good video (only 6 minutes - the running “jitterbug” happens at 3:45):


While not featuring the jitterbug, here too is a 20 minute period WWII training introduction video for the position of navigator in one of these aircraft. From the before-flight to in-flight calculations, the video is pretty eye-opening regarding what a navigated plane entailed in terms of navigation efforts in the period, here in the case of an aircraft fitted with a drift meter, “auto-pilot” (whereby the navigator takes flight control of the plane’s heading using a “remote control”), etc. The “ground speed” calculations in particular (shown first at about 13:20 in the film) are particularly telling.

Thank you for these entries!

I find interesting that many mil spec pilots watch were three-handers, while others were chronographs. Not that it’s surprising there was variation, but instead it would be interesting to understand the contexts and decisions that went into deciding where the variations occurred.