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A Review of the Omega Speedsonic f300 Hz Chronograph Chronometer

By LesZ


IF I TOLD YOU there is a watch which is a member of both the Seamaster and Speedmaster families, and which is not a manual wind, an automatic or a quartz, would you believe me? Well, you should, because that's what the Speedsonic f300 Hz Chronometer is. It's a fifth generation Speedmaster—admittedly not a very familiar one—which was first manufactured in 1973 and continued to be available until 1980. It is one of the few models in the Speedmaster family to bear the title "Chronometer"; the others are some limited edition commemoration models, beginning with the 1973 automatic Speedmaster 125 to celebrate the 125th anniversary of the founding of Omega in 1848. Of course the quartz Speedmasters would have easily gained COSC certification as chronometers had they been submitted for testing, but apparently they weren't and so were not designated as such on their dials. (What's that? You didn't know there were quartz Speedmasters? Yes there were, briefly, starting in 1977. And all Speedmasters are considered members of the Seamaster family because they use a case capable of withstanding high pressure, which was originally developed for the Seamaster.)

The Speedsonic is interesting for several reasons. Firstly, it has a hybrid electronic/mechanical tuning fork movement based on the Bulova Accutron design. The incorporation of this movement into the Speedmaster range was a radical departure from the trusty calibre 321 and 861 (manual wind) or 1040 (automatic) mechanical movements hitherto used. Given the importance Omega placed on the NASA accreditation it had received for the Speedmaster after rigorous testing for space flight, why would it now use a movement produced under licence from its fiercest rival for that accreditation? (Bulova tried everything to get its candidate watch (a mechanical chronograph using a Swiss 17-jewel movement supplied by Universal Genève, Bulova's subsidiary in Switzerland) accepted for the space program, including offering to supply them at no cost to NASA. They even tried to apply political pressure by invoking the Buy American Act, which in fact nearly rebounded on them. It was only by including research and development costs that Bulova's own watch met the Act's minimum requirements for an item to be considered as a domestic source end product.) Bulova already had its products on satellites and space craft consoles as timers, but they desperately wanted the publicity that would flow from having the first man on the moon actually wearing a Bulova watch. Accutron Moon Ad

Bulova advertisement aimed at jewellers. For Bulova, so near and yet so far!

There may be several reasons for Omega deciding to use the tuning fork movement, all conjecture on my part. It could be that Omega sought to mollify (or head off) Bulova by using its movement in one of the Speedmaster family. Or perhaps Omega considered the superior accuracy of the tuning fork and the obviation of the need to wind it (some astronauts forgot on occasion to wind their Speedmasters) would make it an ideal candidate for future space missions, and they wanted to have their own version available in case NASA's requirements changed and a new round of testing for accreditation would be ordered. Or maybe Omega became aware of the popularity of the Bulova Accutron among mission control personnel because of its accuracy and smooth sweep second hand. Or perhaps it was the fact that L. Gordon Cooper flew into space with two watches in 1963—a Speedmaster and a Bulova Accutron Astronaut, which showed 24-hour time. I really don't know. Maybe they were just adopting the latest technology like many other manufacturers, such as Longines, Movado, Universal Genève, Certina, etc. — the latest, that is, until quartz came along a few years later.

Another reason the watch is interesting is that it's the first in the Speedmaster family to incorporate both date and day indicators, and because of this it's also the first to have the three subdials at 6,9 and 12 instead of the more usual 3,6 and 9.

First Acquaintance

WHEN I WALKED into my local Citizen repair agent's shop to have the leather strap on my Navihawk replaced with a metal band, I had no intention of buying a watch. However, cunningly placed in easy view of finger-tapping waiting customers is the 'pre-loved watches' cabinet. This contains all sorts of goodies to trap the unwary enthusiast. As my eye wandered lazily over the casually displayed stock, it came to rest with a jerk on something that bore a strong resemblance to a Speedmaster, yet looked like no Speedmaster I had ever seen before. The hand-written label stuck to the watch said: "V. Rare—Collector's Item". I looked at the dial more closely. 'Omega Chronometer—Speedsonic—f300 Hz'. The small seconds hand on the subdial at 12 o'clock seemed to be making its steady way around with uncanny smoothness. Hmmmm. Must be a tuning fork movement. I had heard of the Accutron of course, but had only rarely seen one. They weren't very plentiful outside the United States. To be honest, I wasn't all that enamoured of them, particularly the Spaceview, with all its insides on display. I asked if I could see the Omega more closely. The watchmaker, sensing what I like to think of as a kindred spirit (although in all probability the term "patsy" was passing through his mind), carefully withdrew it from the cabinet and passed it over. Speedsonic DialThe first thing that struck me was how incredibly large and heavy it was. It felt (and looked) like a square billet of solid stainless steel, but with the mass of gold (I wish!). By comparison the bracelet felt quite light, although it looked solidly made. The dial was satin finished in charcoal grey, with contrasting matt black subdials. All hands and markings were stark white, apart from the hour markers which had that slightly yellow vintage-tritium-almost-past-its-use-by-date look. It had a tachymetre scale running around the dial like the normal Speedie Pro, but under the massive hesalite crystal instead of exposed on the bezel (similar to the Speedie MkII, III and IV. Hesalite is a very strong, very clear acrylic known as "armoured glass".) Overall the dial was not quite as legible as the Moon Watch Speedmaster, being a little more crowded, but it was still very good in the readability department. I held it up to my ear. I heard a faint low hum from the vibrating fork (at 300 Hz, of course), and if I listened very carefully, I could also hear an even fainter high-pitched whine. I didn't know it then, but this latter noise was the sound of the click blades pushing on the teeth of the index wheel at the rate of 300 pushes per second. The rest of the gear train hangs off the index wheel.

I pushed the top chrono button which, like its brother and the rather small crown, gained some protection against knocks by being recessed somewhat into the case. It needed a firm push before engaging the chrono mechanism with a very definite 'click'. The large centre sweep second hand started its majestic journey around the dial, just like one of those electric clocks you used to see in factory canteens, Government offices and public libraries. The minute recorder slowly emulated it, progressing sedately from minute to minute (no jumping minute hand here), and the hour recorder followed suit at 1/24 its speed. (If you want to see what I saw, click here. It's a 1.33mb download and not quite as smooth as in real life because of the digital camera's sampling rate, but you'll get the general idea. As a bonus you can also hear some Australian bush birds in the background.) Another push and firm click of the top button and the recorders stopped dead in their tracks; a similar push on the bottom one and they all reset to zero quicker than the eye could see. I examined the massive steel case, with its sunburst brushed pattern on top and gleaming mirror finish on the chamfered top and bottom edges of the sides. Apart from the slightest of dents in the bevelled edge of the screw-in back, it looked as if it had just come out of the factory. I tried to subdue my stirrings of interest. I strapped it on. "Look at that," he said, "perfect fit. It could have been made for you." "Hmmmm," I said, trying to sound unconvinced. "Although, it looks in nice condition." "So it should," he said. "It's just come back from a complete overhaul at the Omega factory in Switzerland. Of course, it carries a one year full guarantee." The stirrings of interest became wellings. "Funny thing, though" he carried on. "You see that ding in the caseback? I could've sworn it didn't have that when I sent it. I reckon they must've got it switched somehow in the factory." A likely story, I thought—but I said nothing. I was wondering how much I could reduce his price on this "v. rare collector's item".

Knowing next to nothing about the longevity of the Accutron movement, I decided to do a bit of research before committing myself to purchase. I remembered the old ads from the 60s showing a man just missing his bus, and the promise that "with an Accutron you'll never miss the bus again—it's guaranteed to be within a minute a month! That's 99.9977% accurate!" I didn't want to miss the bus on the Speedsonic, but I didn't want to be lumbered with a lemon, either. So I logged into the 'net, loaded my favourite search engine, typed in "Accutron", pressed 'enter' and bingo! Number one on the list was something called "The Accutron Watch Page". Sounds promising, I thought. And that's how I came across Rob Berkavicius and his wonderful website, devoted entirely to tuning fork watches. And he lived in Perth, Western Australia! He had to be an OK guy. I tried to absorb all the information on his site, and decided to send him an email describing the Speedsonic, the price asked, and asking what he thought. Pretty soon he sent his reply: yes, it was a collector's item; these watches tended to either keep running well or not run at all; the price asked was reasonable given the factory overhaul; and I should run down to the shop straight away and buy the watch! Thus reassured, I did just that (after some suitable 'negotiation').

Living with the Speedsonic

Speedsonic side viewFOR THE FIRST DAY OR SO it felt like I had a bar fridge strapped to my arm. During the 70s it appeared for all the world as if Omega were trying to design the heaviest, squarest and thickest watch cases ever made, and with the Speedsonic I think they very nearly succeeded. On the kitchen scales it weighs in at 150 grams (5.3 oz) complete with bracelet; from front to back it measures 15mm (19/32"). The band needs to be adjusted fairly tight to stop the watch from going into orbit around your wrist. In time one gets used to it and other watches feel ridiculously lightweight. The rounded corners of the tonneau case help prevent it catching on shirt cuffs, and to my eye the dial design is restrained enough for it to be worn with a business suit. A night at the opera would demand something more elegant to complement the tuxedo.

Speedsonic band & clasp

The (original) stainless steel bracelet has three links in each row, the outer two being solid and the inner one folded. It tapers in width from 22mm at the vestigial lugs to 15mm at the standard folded clasp. Although it has no fliplock the clasp has a reassuring feel and has never opened inadvertently on me. The bracelet pulls the occasional hair, but apart from that it's comfortable.

The screw-in caseback is totally devoid of any markings on the outside, but has the usual Omega marks on the inside, along with the model and case reference (more about this later).

You can see from the photos (above and left) that the crown is not in the same plane as the pushers. This is because the chronograph mechanism is not of the integrated type with a column wheel, but is modular. The watch is actually made up of three modules: the oscillator module, the mechanism module and the chronograph module, this being mounted on the dial side of the movement (on the front of the pillar plate). The chronograph module was designed and manufactured by Dubois Depraz SA, who still do this sort of work for watch manufacturers. The whole watch is a complex piece of machinery, and should only be worked on by people familiar with, and experienced in, repair of these models. Even battery changing should be left to the experts.

As previously stated, the chronograph mechanism is very positive in its action and works well. However, I find the continuously-incrementing minute accumulator harder to read at a glance than the jumping-type one on my Breitling Navitimer. Talking of which, I wish the Speedsonic had a slide rule like the Navitimer rather than the tachymetre scale. Is there anything more useless than a tachymetre? (Yes, a bezel with N, E, S and W marked on it.) Hands up all those who have used a tachymetre more than once, when you first got it. As I thought, not many—just the production engineers. After all, there's only so many occasions when you want to measure your speed by driving at a steady rate between two points exactly 1km or 1 mile apart. (I did, once, and discovered my speedometer was reading 10% fast.) Even a pulsometer would be more fun, and you could check your pulse during boring meetings to see if you're still alive.


As the watch had been overhauled by Omega I expected accuracy to be at least within the guaranteed 2 seconds a day, and probably better. I was disappointed to find it running at around +3 seconds/day. However, this was no problem for my repair man. "Varies with temperature," he informed me. (It was now summer in Australia, a far cry from autumn in Switzerland when the overhaul had been done.) "Leave it with me for a day or so -- it can be a fiddly job." I left it with him, and when I got it back it was within 0.5 sec/day. I have found out since that it is possible (with some patience) to tweak these watches to between 1/4 and 1/2 second a week, although I suspect it involves having your own electronic timing machine and an inexhaustible supply of case-back O-rings. There's no doubt that temperature does affect the timekeeping however, although not by more than a second or so. It's about the only thing that does affect it, as there is (theoretically) no positional error (see later).Graph - daily rate

This graph shows the daily variations of the Speedsonic in seconds per day measured over a period of 32 days of normal use. It can be seen that the maximum daily gain is 1.5 seconds; on 14 days there was no gain or loss at all. The average gain for the period is 0.51 seconds per day. The only variable I can think of that might account for the change in rate is temperature.

Water resistance

According to Omega the Speedsonic has a water resistance of 6 atmospheres or 60 metres. However, they also state that "such watches are not supposed to be used underwater since they are not "skin-diver" models. The indicated water resistance is made in order to avoid infiltration of dust and water when using the watch under daily normal conditions. For use underwater, it is recommended to use exclusively a real skin-diver watch, clearly having the required protection of a minimum 120 metres and more." I'll take their word for it. Other Speedmasters have water resistance of 3, 6 or 12 atmospheres, depending on the model. Take my tip—play safe and don't get yours wet.

Time, day and date setting

This is easily accomplished with the 3-position non-screw crown. In its first position (snug against the case) it rotates freely. Pulling it out to the first detent (position 2) and turning it clockwise allows quick adjustment of the day, and anticlockwise adjustment of the date. Pulling it once more to the second detent (position 3) hacks the movement and allows adjustment of the hands. When hacked, the movement takes a second or so to stop, but this is compensated for by it taking the same amount of time to start again. Apparently the watch should not be left for long in the hacked state as the current draw increases dramatically, unlike a normal quartz analogue which can be stored with the hands stopped to conserve the battery. The automatic day and date change starts to takes place around 1am and proceeds in a leisurely fashion until completion around 2.30am.


The hour batons originally had copious amounts of tritium as did the inserts in the hour and minute hands, but sadly much of it has gone walkabout. A faint glow is still discernible throughout the night, but it's hardly in the Panerai class. Omega reckon the tritium is only effective for 10 years, after which "it is necessary to replace the dial or have a re-conditionning made if more luminosity is required."

The Movement

Accutron forkIt's the movement that makes this watch special, and so it deserves a section to itself. The heart of the movement is of course this little fellow (right). Well, not exactly, because the Speedsonic uses a modified fork design with additional weights near the magnets. These give superior performance by reducing positional error to virtually zero. Another difference is that in the early design (below left), adjustment of the fork's natural frequency (and hence the timing) is accomplished by turning weights on the inward-facing ends of the fork cups. In the modified design (below right) this is accomplished by rotating the weights mounted on the bottom of the tines by equal amounts in opposite directions. Omega also claim that by repositioning the driving click near the bottom of the tuning fork, the effects of wear are minimised leading to longer correct functioning of the indexing mechanism.
218 forkesa fork

So how does it work? Well, to put it simply (very simply), the battery provides current to a transistorised circuit, which then pulses it at 300 times a second through many turns of fine wire forming a coil within each tuning fork cup. The coil of course acts like a pulsing electromagnet, causing the tines of the fork to resonate at 300 Hz. As the tines vibrate, a tiny finger or 'driving click' attached to a tine moves backwards and forwards over a toothed wheel—the 'index' wheel—pushing it round tooth by tooth. A 'stationary click' situated further round the wheel also bears on it and checks its position, while preventing it from moving backwards. The index wheel, the first in the gear train, has 300 teeth and thus makes one revolution in a second. This rotary motion is conveyed through the normal system of gears and pinions to finally turn the hands.

Speedsonic movementAs you can see, the view after taking the back off a Speedsonic is not particularly exciting. The dominant feature is the battery, of which more later. The coils of copper wire forming the electromagnets are plainly seen, as are the poise-adjusting weights at the foot of the tines. The movement has 12 jewels, and is 'unadjusted'. It was made by the Swiss firm Ebauches SA (ESA) under licence to Bulova. These ESA movements use index wheels made by Bulova, and are probably the finest tuning fork movements ever made. They were certainly expensive to make. Omega sent their movements for COSC testing and so they received the 'Chronometer' certification. Exactly the same movement (part of the "Swissonic 100" series) was used for the Longines Ultronic and the Certina C-Tronic, among others. Only 21,000 of these movements were made, between 1972 and 1976.

The Accutron movement embodied two major advances over all electric/electronic balance wheel movements made hitherto. The first advance was of course, the use of a tuning fork as a resonator. Instead of the lowly 2 or 3 Hz of a balance wheel, the tuning fork resonated at 300 Hz (or 360 Hz in the case of the original Accutron), giving much more stable and accurate time measurement. (Compare this with the usual quartz frequency of 32,768 Hz and you can see why quartz is so damn good.) Secondly, and perhaps more importantly, the use of the solid state transistor to rapidly control current flow was a major breakthrough. The Achilles heel of the Hamilton and similar electrics was always the contacts used in the make-and-break circuitry; they were subject to premature burning out and were thus unreliable. The Accutron did away with all that and replaced it with solid state reliability.

The early Accutrons were designed to use mercury batteries which provided an operating voltage of 1.35 volts. As the world's supply of mercury batteries diminishes for environmental reasons, these models can in most cases be kept going by using silver oxide batteries of 1.5 volts, although some adjustment of the watch might be needed. The ESA movements (such as that used in the Speedsonic) were designed to use either mercury or silver oxide, and if serviced according to specifications should run happily on either without any further adjustment. Rob B's Accutron website explains all this (and much more) in great detail. Rob also suggests servicing should be carried out every 5-10 years.

Speedsonic Variants

Speedsonics came in various shapes and sizes, as shown below. For some reason the three models other than mine (third from left) had short, skinny hands. I may be biased but I prefer the look of mine, although the one on the far right is OK too (with thicker hands!).
speedsonic variants

Omega Customer Service

I have to mention the excellent service provided by Omega Switzerland where, if you send them the reference number (on the inside of the caseback) and the movement number, they will furnish you with details about your watch from their archives. In my case the reference number is ST 188 000 2. In Omega parlance, the ST means the watch case is stainless steel; the first numeral (1) signifies a leather strap was fitted originally; the second numeral (8) means a quartz or tuning fork chronograph mechanism; and the third (8) means a chronometer. Note that bit about a leather strap; my watch has the correct bracelet for the time (reference ST 1162/172), but did it leave the factory with it or was it a replacement for a worn leather strap? Or did they swap the caseback at the factory during the overhaul after all? Is someone walking around with my ding-free caseback? And should it have a seamonster on it? For the time being, these questions must go unanswered.
(I was gently reprimanded by the ever-helpful Mr John Diethelm of Omega Public Relations for calling their trademark design a 'seamonster'. "We have never used 'sea monsters' ", he wrote. "It is clearly defined that the emblem used by OMEGA is a 'Seahorse' like those that were pulling Neptune's chariot over the seas!" Sorry, John.)

My watch was delivered to the London, UK Omega agents on 9 September, 1975. That particular model was offered in Omega's International Collection from 1974 to 1980. The retail price with leather strap in Switzerland was Sfr 895 (about AUS$850 or US$545)—quite a tidy sum in 1975 (and nothing to sneeze at today, either).


THE SPEEDSONIC MARKS AN INTERESTING STAGE in the development of the Speedmaster. The reason behind fitting it with a tuning fork movement may never be known—be it fashion fad, cutting edge technology, or big business politics. At the time the decision was taken to proceed with production (say 1971, as the Speedsonic was first produced in 1973), the Apollo space program was still in progress. Indeed, the last Apollo mission to the moon (Apollo 17) took place in December 1972. In 1970, thanks to pressure by the CEO of Bulova, General Omar Bradley, 17 manufacturers were invited by NASA to submit chronographs for testing. Among the list were Bulova, Omega, Breitling, Rolex and Seiko. Those watches that passed the tests (the same ones the Speedmaster had been subjected to in 1965 along with Longines and Rolex) would be put on the Qualified Product List. Ultimately only the Bulova was tested and it failed to qualify, putting an end to Bulova's dreams of a publicity goldmine. Had the Speedsonic been created to pass these tests? If size and weight are anything to go by, it would have passed with flying colours.

Watches with tuning fork movements are relatively rare these days, and Speedmasters with tuning forks even more so. Omega went on to make Constellations and other models with the f300 Hz movement, and even used an f720 Hz movement which delivered even greater accuracy. It had other innovations too, like a completely encapsulated index mechanism and no direct connection between the index wheel and the rest of the gear train! It used a magnetic coupling which in theory had several benefits over mechanically-coupled gear trains, but I understand in practice it became a bit finicky.

So I regard the Speedsonic as an interesting momento of a technology that deserved its place in the sunshine, but was soon overshadowed by the mushrooming giant, quartz, which did a better job at a much cheaper cost. I've found it to be comfortable (once I got used to the weight), reliable, accurate, and easy to adjust for short months and daylight saving time. It has what I call "rugged good looks", in the Speedmaster mould. I must admit I'm a little worried about possible shortage of spare parts for this particular model (I believe parts for Bulova Accutrons are easier to come by), so I treat it carefully but still wear it on a daily basis. And after all these years, the s-m-o-o-t-h sweep second hand still fascinates people......and me!

Technical Specifications

Model:  1975 Omega Seamaster Speedsonic Chronometer Chronograph with day & date, Model no. ST 188 0002. Signed in 6 places: dial, crystal, crown, inside of caseback, clasp, movement.

Movement:  Omega Calibre 1255 electronic tuning fork with 12 jewels (made by ESA under licence to Bulova).
Vibration frequency: 300 Hz
Quality factor: 2700
Position error: <1 sec/day
Thermic coefficient: +/- 0.25 sec/day/degree C
Isochronism (dV/V = 10%): 1.5 sec/day
Max. disturbance acceleration: ~100 g's
Residual effect (H = 60 Oersted): ~1 sec/day

Accuracy: better than 1 minute per month.

Battery: Mercury 343; Silver Oxide 344, SR1136SW. Consumption: <9uA. Battery life: ~15 months.

Case: Stainless steel, screw back, water resistant to 6 atmospheres (60 metres). Size 43mm x 43mm excluding 5mm dia. crown. Weight (with s/s bracelet) 150 grams.

Crystal: Hesalite (acrylic).


Much of the information in this review has been gained from two sources: the aforementioned "The Accutron Watch Page" website compiled by Rob Berkavicius, and the recent publication "A Time Capsule: Omega Speedmaster - The story of the first watch in Outer Space" edited and written by Kesaharu Imai and published by World Photo Press. From that publication come the photos of the ESA movement and the Speedsonic variants. From Rob's site come the photos of the early and modified tuning forks. The Bulova advertisements come from Tom Mister's website Dashto Horological Services. The other photos and the movie clip were taken by me using a Sony Mavica FD-83 digital camera.

© Les Zetlein 1999

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Last updated 8 June 2008

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