What is the Most Accurate Watch in the World?

If you are interested in high-accuracy timepieces then you probably want to know which is the most accurate watch in the world. That's how my habit / hobby began. And, to be clear, the interest lies in intrinsically accurate watches - not in watches that manage persistently to display the time correct to within about a second or so because of some external time sync.. It is, of course, perfectly valid to argue that most people don't need the intrinsic accuracy of a HAQ over the sync'd accuracy of a smartwatch, but this hobby isn't about 'need' or arguments over the relative merits of this watch or that. This is all about self-contained, high-accuracy timepieces. The 'need' of a HAQ collector may be very real indeed, or may be principally driven by OCD, but no counter-argument or alternative interpretation of adequate, practical accuracy can diminish the hunger for truly accurate watches. After all, how many owners of dive watches 'need' 1,000m+ rating (or, indeed, any water resistance rating at all?). And so we search the web.

The first page of a Google search currently throws up several links to the Bulova Precisionist. I found these, too, when I first began looking for the answer to this question. What's often missing from the articles on the Bulova, however, is the final piece of the sentence: "The most accurate watch in the world... with a sweeping second hand". You see, it's not particularly clearly stated on Bulova's site and it could be interpreted to mean that their watch is both the world's most accurate and has a sweeping (or 'gliding') second hand. And the confusion caused by the way Bulova present the statement evidently carries over to those sites that fail to repeat the second part of the statement and instead claim that Bulova's Precisionist is absolutely without doubt the most accurate watch ever made. Let's be clear: it isn't.

Bulova specify their P102.12 and P102.10 high frequency (HF) movements to +/- 10 seconds per year (SPY) and frankly you'll be lucky if any given example holds to that spec. for very long. The movement is unadjustable and once the cyrstal oscillator (XO) ages, the change in its thermal performance will mean it will never hold to 10 SPY again. Still, 10 SPY is a good figure. A watch that can hold to that rate is an accurate watch indeed. So, which watches can?

Among the HF contenders, Seiko's Y301 movement, used in the Pulsar PSR 10, also claims 10 SPY. Each of my two PSR 10s is currently running closer to 70 SPY, however. Crystal ageing, again. By the time the Bulovas are as old as the PSRs, I expect their performance will be similar.

Casio, Citizen, Junghans and Omega all offered HF watches in the megahertz range and all had rate trimmers. This means that they should, in theory, still be able to meet their advertised rates. In the case of the Citizen Crystron 4 Mega, this was generally 5 SPY, although the very first, limited edition release was rated at 3 SPY. The Casios were rated at either 10 or 15 SPY, depending on the model, and the Omega Marine Chronometer was rated at 1 SPM (12 SPY). I don't know what the stated accuracy of the Junghans Megaquarz was, but it is unlikely to have exceeded the 3 or 5 SPY figures of Citizen's watches.

The last of the megahertz-range watches was released in about 1980 and the modern crop of HF movements are either completely unadjustable or can be adjusted only a few times, in crude steps, by pattern cutting. So, what else is available, today, in the 10 SPY (or better) range? Thermocompensated (TC) movements are offered by Seiko, Citizen and ETA in large numbers, whilst Omega and Breilting have their own offerings and small, independent brands such as Hoptroff, Morgenwerk and DeHavilland also have products on the market. Citizen and Seiko both make movements in both 5 SPY and 10 SPY variants, although 5 SPY is much more the 'bread-and-butter' of Citizen than Seiko. For Seiko, 5 SPY movements tend to be special editions. ETA's movements are generally spec'd to 10 SPY, although afer being modified by Breitling to meet the brand's 'super quartz' spec., the stated accuracy drops to 15 SPY.

The adventurous HAQ collector may try to pick up a Texas Instruments EZ430-Chronos and programme it himself. Reports have suggested that these can be made to achieve sub-5 SPY, even down to 1 SPY. But if you are prepared to take a chance on an independent brand that may not last long enough to support your watch into the next decade, then both Hoptroff and Morgenwerk offer TC watches with stated accuracy of 1 SPY or better.

Radio-controlled (RC), GPS and 'smart' watches may all promise accuracy of 1 second per thousand years, but let's be absolutely clear: their base quartz movements are generally no more accurate than the movements of any ordinary quartz watch. Citizen's F150 and F900 are exceptions, as their non-sync'd rate is 5 SPM, but this still falls far short of 10 SPY. Morgenwerk's GPS watches and Hoptroff's 'smart' watches are the real exceptions to the rule, as they both offer accuracy of 1 SPY or better (though some of Hoptroff's lower-cost models are spec'd to a still-impressive 10 SPY). The trouble with most externally-sync'd watches, then, is that they gain (or lose) time far too rapidly to be useful as true high-accuracy watches. You may have an RC watch that picks up a signal at 02.00 and syncs perfectly to UST, but by 18.00, when you sit down to tea, it could be off by a second or so. A HAQ could be off by a second or so, too, at any given time, but if it is a second off today, then you can be sure that it will be a second off every time you look at it for at least a month. It's consistent. You could depend on it as a time reference. Your typical RC / GPS watch just cannot be depended on in the same way. Judging simply from the results I have seen from my RC Citizen, I would not feel confident trusting the time from such watches from about an hour or two after they sync.. If you can be confident that your watch will sync. every day, or every couple of days, then you can be confident that your watch will always have 'about the right time' whenever you look at it. And this is great for some people. With solar-power thrown into the equation, these really are 'set-and-forget' watches. I love my Citizen RC watch for that. But they're not nearly as accurate or precise as they claim to be. An always-connected watch, such as the Apple Watch, may fare better, but Apple's assertion that the iPhone always shows the precise atomic time is just not true. It really does depend on your location and carrier. An should your iPhone be out of juice, out of range or out of order, then even if precise time is supported by your carrier in your location, then your Apple Watch will still be wandering in the realm of ordinay quartz timepieces.

So... for mainstream watches you can get 5 or 10 SPY. For niche products, you could push this down to 1 SPY. But what about atomic watches? Hoptroff offer a small range of watches that incorporate Chip Scale Atomic Clocks (CSAC) and are accurate (in full-power mode) to a second-and-a-half per thousand years. And there it is. That's the highest level of accuracy of any watch in the world, right now. So, let's break it down in terms of what's currently on the market:

1. Hoptroff Atomics (No.1, No.2, No.3, No.10, No.16) - 1.5 seconds per thousand years

2. Hoptroff (No.9, No.11, No.14, No.15 & Hotblack 'Calibre' editions); Morgenwerk (M1, M2, M3) - 1 SPY

3. The Citizen / Chronomaster (all quartz / eco-drive models) - 5 SPY

4. Grand Seiko (all quartz models); ETA (Precidrive range (e.g. Certina DS-2, Christopher Ward C7, Tissot PR 100)); DeHavilland (all models); Hoptroff ('normal' Hotblack series) - 10 SPY

5. Breitling (all quartz models) - 15 SPY

6. Omega (X-33) - 20 SPY

Bulova, of course, have their 10 SPY Precisionist, but, as already explained, this is both unadjustable and unlikely to hold true to its spec. for very long. DeHavilland's range of 10 SPY watches is quite niche, but may present an interesting alternative to the usual suspects, especially for pilots.

If you want a watch with a Swiss HAQ movement (of current production), then you may have to look carefully at the detailed spec. sheet. Some brands tell you quite clearly if one of their watches is a HAQ; others don't. Certina, Christopher Ward, Tissot and even Invicta have used (or currently use) ETA's Precidrive movements. Some even come with COSC Chronometer certificates, but this just means that the movement has been tested and certified - not that it is any more accurate than a Precidrive movement without a COSC certificate.