# Zenith Caliber 707 No. 601



## arezzo

_Neuchatel Observatory
_


The Zenith 707 caliber nicknamed internally as the "Kartoffel" or potato because of its unique shape was designed in late 1961 early 1962 and built in 1963 exclusively for Observatory Competitions to replace the venerable Calibre 135. The 707 designation comes from the Observatory Competition requirements for wrist watch movements that they be less than 30mm in diameter or 707 square mm in total. It is interesting Zenith decided to call this calibre 707 when the actual area of the movement is 685 square mm.



The movement was the last one designed for the Observatory Competitions from 1963 to 1967 and was never commercially sold to the public. Think of it as a factory Formula 1 engine and therefore its construction and design is built purely for efficiency, competition and performance without any fuss. The development team was headed by Aurelius Mayor who was the Technical Director of Zenith at the time also consisted of Rene Gygax, Jean-Pierre Vuille, Paul Favre and Jean-Pierre Sunier.



The winding and time-setting is done via a crown on the back and the movement has a power reserve of 36 hours running at a frequency of 28,800 bph. Each component has been designed to reduce friction and lubrication is optimized. The teeth of the wheels are tapered, all the pallet stones are of the best quality highly polished 21 rubies to reduce friction. The movement has a thickness of 5mm, a Guillaume balance wheel similar to the Caliber 135 measuring 13.8mm x 0.99mm, a lever escapement, a double anti shock Duofix system for the Balance Escapement and a Nivaflex balance spring wound 15 times with a thickness of 0.16mm and a length of 46mm. The thin balance bridge is secured by 2 screws on one side and one screw on the other facilitates in the observations of the balance spring.



There is conflicting information on how many of these movements were made, some sources quote 250 and others 200. Regardless only 127 were entered into the Neuchatel Observatory competitions for wrist watches.


At the 1964 Neuchatel Observatory competitions No. 558 adjusted by Pierre Gygax came first, No. 521 adjusted by Jean-Pierre Vuille came in third, No. 527 adjusted by Jean-Pierre Sunier came in ninth and No. 515 also adjusted by Jean-Pierre Vuille came in tenth. Therefore out of the top 10 watches of the year 4 were Zenith Caliber 707 movements.


*At the 1965 Neuchatel Observatory competitions movement No. 601 of the Zenith Caliber 707 adjusted by Rene Gygax would come in first and also again in 1966.

*


More Pictures













Highly recommend reading this post which highlights the struggles of Grand Seiko against the Swiss at the Observatory trials

https://www.watchuseek.com/f21/three-kings-grand-seiko-919759.html

S

Credits and Thank You: Zen from Forumamontres, Hartmut Richter, Manfred Rossler and his book on Zenith, Bruno.M1, RDL, Heffels, relojes-especiales, Google Images


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## Hartmut Richter

What a wonderful watch! Probably the only one of its kind. From the book onto your wrist - you must feel special! (At least I would). Thanks for the write up and the pictures.

Hartmut Richter


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## D N Ravenna

That is really wonderful! Thanks for sharing the pictures and history!

:-!

Dan


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## omeglycine

What a wonderful post and special, special watch. Thank you for sharing!


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## sempervivens

Beautiful post, thank you for that. 

It does look like a potato. 

Do you know what the black blocks in the seconds dial are for?


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## Hartmut Richter

That is the original dial used in observatory competitions or COSC tests. The reading of movements is done by machines on an optical basis so they read and compare the exact time elapsed between the seconds hand going between the two blocks and it doing so again (AND the other hands being in exactly the same position, of course!).

Hartmut Richter


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## WTSP

Wow, that's incredibly strange, but fascinating! Arezzo, with this Zenith Potato movement you have definitely reached a pinnacle in watch collecting! Such a raw construction would never see the light of day in today's aseptic horological climate. It almost looks like an Artya watch. Congratulations! I hope the Nato strap makes it wearable without putting too much stress on the crown stem.


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## arezzo

Thank you for your kind words, its interesting how in the Rossler book it says the watch can't be worn because of the crown on the back, on the contrary I've been wearing the watch regularly on the Nato and its really comfortable. It would be cool if Zenith did a limited redition of this piece which won the Neuchatel trials 2 years in a row, I have received so many compliments on the watch and some of my WIS friends get really surprised when I tell them its a Zenith.



WTSP said:


> Wow, that's incredibly strange, but fascinating! Arezzo, with this Zenith Potato movement you have definitely reached a pinnacle in watch collecting! Such a raw construction would never see the light of day in today's aseptic horological climate. It almost looks like an Artya watch. Congratulations! I hope the Nato strap makes it wearable without putting too much stress on the crown stem.


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## arezzo

*CORRECTION*

I wrote in my post "At the 1965 Neuchatel Observatory competitions movement No. 601 of the Zenith Caliber 707 adjusted by Rene Gygax would come in first and also again in 1966. "

the above statement is wrong and I wish to correct it, the movement Z-601 was entered in the 1965 Neuchatel Observatory trials, adjusted by Rene Gygax and achieved a Premier Grading with a N-Score of 5.58 and ranked 109 and was also entered in the following years trials of 1966, adjusted by Rene Gygax and achieved an N-Score of 4.39 and ranked 97.

*Credit and thanks*: http://www.observatory.watch/

*Alexander Pope *wrote: "To err is human"

*Peter Drucker* wrote: “We now accept the fact that learning is a lifelong process of keeping abreast of change."

🙏

S


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## WTSP

By the mid sixties things seem to have become very competitive. Perhaps the Longines 360, GP Gyromax and Seiko were stronger. I forget whether the timeframes so of coincide for those.


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## bwh21335

very unique and interesting watch!


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