Breitling Navitimer 1 Automatic 38 and the History of the Slide Rule Watch

Breitling’s first Baselworld under Georges Kern has brought some interesting new concepts to light. Some, like the Navitimer 8 collection, are an easy step away from what we have seen before. Others, like the colossal Navitimer Super 8, are a little more challenging. The Navitimer 1 family would seem to be familiar territory, the dial layout being what we would expect, even if the logo has been tweaked; but buried amongst the references is a quite unexpected watch, the Navitimer 1 Automatic 38mm.

Originally trailed as a “women’s” watch and then sensibly updated to be “unisex”, this is a Navitimer without a chronograph function. This is not the first three-hander to bear the name, but the only previous example was a 1950s dress watch with a date window and no rotating bezel. The 1952 ref. 2508, listed as a Chronomat (although not on the dial text), is a further early example of a dress/tool watch.

The most eye-catching feature on the new 38mm is the slide rule, especially on the blue dial variant, which appears clearer without the sub-dials. The smaller case avoids the acres of empty space and, along with the beaded bezel, appeals to the vintage watch lover in all of us. Importantly, with this watch, Breitling challenges the assumption that slide-rule watches must also be chronographs. And, on that note, we take you on a journey through time to where it all started…

Do the Math

In the year 1550, Scotland was in turmoil. The English were retreating from the borders after an unsuccessful attempt to force a union, leaving the Scots in danger of control from France – an alarming prospect for the Protestant nation. John Napier was born into this uncertainty, the first son of a prominent family, whose father would go on to run the Scottish Mint. Napier studied at Edinburgh University but never graduated, leaving early to pursue his education in Europe.

Returning in 1571 to find his father imprisoned and the family home occupied due to civil war, Napier took refuge on one of the family estates and applied himself to the study of mathematics.

His passion for astronomy required time-consuming calculations of very large numbers which fuelled his search for a simpler method. Twenty years of research led him to logarithms which were first outlined in 1614. In essence, logarithms are the opposite of exponentials, where the intervals on a scale would get closer together the higher the value rather than further apart – both the Richter Scale and the decibel scale are examples. He went on to invent a mechanical aid for using logarithms in calculation called “Napier’s Bones”, his active mind also leading him to invent weapons of war including mirrors for burning ships at a distance, area-effect artillery and primitive tanks.

The evolution of Napier’s Bones into something more ruler-like was done by Edmund Gunter (1581-1626), Professor of Astronomy at Gresham College, London, mathematician and inventor of scientific devices including the “Gunter Chain” used in surveying – 100 links, 66ft in length (side note: one chain, 22yrds, gave us the length of a regulation cricket pitch); the “Gunter Quadrant” used to find the hour of the day; and the “Gunter Rule”, a logarithmic ruler used with a pair of dividers to make calculations. Variants of the Gunter Rule were in regular use aboard ships until the end of the 19th century.

Magic Stars

The first actual slide rule was created by William Oughtred, a Church of England Rector, Fellow of Kings College Cambridge, teacher of mathematics and a contemporary and correspondent of Edmund Gunter. He simply took two Gunter rules and slid them alongside each other, eliminating the need for dividers. He also invented a circular slide rule but became embroiled in a dispute over priority with one of his students. His mathematics and the instruments that went with them were described in his book The Circles of Proportion and the Horizontal Instrument, 1632. Oughtred also invented a new kind of sundial which still bears his name.

Much of the advanced mathematics of the age was devoted to astronomy and the trigonometry involved with laying out accurate sundials, hence the slide rule and timekeeping have been linked since the beginning. Oughtred was also included on a panel to assess the claims of a Captain Marmaduke Nielson to be able to find longitude at sea by astronomical means. As we know, the awarding of the prize to Harrison over 100 years later means that Nielson’s method did not work. In later life, Oughtred went on to write a short book on watchmaking and two of his sons went on to become watchmakers.

Over the centuries, the slide rule was refined with additional functions and scales added. New versions were developed by the likes of Isaac Newton, Matthew Boulton and James Watt. The final form that we would recognise today was designed in 1850 by a French army officer, Amédée Mannheim.

With a circular slide rule being such an early innovation, it would seem natural to combine the rule with a time-telling device, but it took until the late-19th century for this to happen, with the appearance of the Meyrat & Perdrizet French pocket watch with slide rule.

Wristwatches didn’t appear for another half century, the onset of the Second World War spurring the production of technical wrist instruments but then, as with buses, three came along at once.

The Three Rules

While not the first to apply for a patent, the first to produce a product for sale in 1940 was Mimo, a company later to be absorbed by Girard-Perregaux, followed almost immediately by Breitling, and four years later by Juvenia. Each watch interpreted the slide rule slightly differently.

On its three-hand watch, Mimo used the classic logarithmic scales that increase clockwise, referred to as C and D. The Breitling used one scale that increased clockwise and one that increased anticlockwise, referred to as C and C1. This may have been to avoid copyright infringement but also the C1 scale could be used with the chronograph as a tachymeter.

Juvenia also produced a three-hand watch but created a bulbous ring around the edge of the watch crystal to magnify the scales. Theirs had three scales C, C1 and D1, that is… two increasing anti-clockwise and one increasing clockwise. All could be used for multiplication, division or finding square roots while the latter two could also work out reciprocals.

It seems that these three watches effectively closed the patent window, with no other brands entering the market for the next 20 years. Breitling’s combination of chronograph and rule proved decisive and the Chronomat became a great success while the others slipped into obscurity. In 1952, it offered a new scale, similar to the Mimo rule but including a third scale for time and distance calculations. This watch was targeted directly at pilots and the new rule would have been immediately familiar to them as it copied the layout of the E6B circular pilot’s calculator used for pre-flight navigational calculations – a calculator still used to this day for training purposes. This watch was, of course, the Navitimer, which has set the template for pilot’s slide rule watches ever afterwards.

Once the initial patents had expired, a wave of other slide rule watches were produced targeting pilots, engineers or anyone who needed to do math, from the likes of Ollech & Wajs (Selectron Computer), Heuer (Calculator), Seiko (6138-7000) and Fortis (Easy Math). The pocket calculator had yet to reach the mass market and slide rules were still much used in daily working life. The shift from analogue to digital watches in the early-1970s didn’t displace the circular slide rule either, Breitling produced Navitimers with both LED and LCD displays and today’s manufacturers of ana-digi pilot’s watches still include them as a feature.

With all aspects of modern aircraft navigation computerised and a scientific calculator just a visit to your mobile app store away, slide rules are another feature of a watch that is nice to have but rarely used. Rather, they link back to a time when a watch was a tool your life genuinely depended on.

It is interesting to note that, unlike the rest of its Navitimer 1 family, the 38 automatic loses its innermost scale, the bezel becoming more like the original Mimo 1940 version. It may not be the first Navitimer without a chronograph, but it is the first Navitimer to have a slide rule not based on the E6B flight computer. Under Georges Kern, it seems that Breitling can break the rules and adopt novel ones.

E6B “Whizz Wheel”

Invented by US Naval Reserve Pilot Philip Dalton in the early-1930s, the E6B was named after its original part number for the US Army Air Corps. It was used to calculate ground speed, fuel use, wind drift and several other problems.

A casualty of history and the forgotten hero of so many important events, the crew of Apollo 11 –NASA’s Lunar Lander space vehicle – carried slide rules, for the first time in history, into space and onto the moon in July 1969. The slide rule of choice for Neil Armstrong, Buzz Aldrin and Michael Collins was the aluminium pocket Pickett 600-T Dual Base Log Log. The slide rule’s place in space travel is confirmed by retiree Norman Chaffee, who worked on the spacecraft propulsion system, and says: “We went to the moon with slide rules. I didn’t even have my first full-function calculator until 1972.”

Thankfully, popular culture does give a small nod to the slide rule’s space race. The movie Apollo 13 shows engineers in the background using the now lesser-seen tools. And, offering genuine legitimacy, in episodes of Star Trek broadcast in 1966/67, Leonard Nimoy’s Spock can be seen holding and using an E6B.

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