Let's start with the Zenith Extra Prima. For this, I am using French Forum A Montres and Manfred Rössler's Zenith book as primary sources.
Rössler has extensive list of images of Zenith movements. But not the 19" ligne, 41,3mm movement in this watch that has 68-21 written under the balance wheel (and visually resemble Zenith Cal 69). The book doesn't have photos, or otherwise mention Zenith Extra Prima either (caveat emptor, it may still be hiding somewhere there). In the movement table however one can find 68-21: 19" ligne, 41.3mm wide, 6.45mm thick, 21j, 18000bph movement manufactured between 1961 and 1962 with total 6000 manufactured. This largely corresponds with information found from [
NAWCC] and [
WUS] threads for this PW.
But the story doesn't end here. In fact, it appears to start in 1906. It was also hiding in 'plain' sight at French speaking Forum A Montres[
FAM1][
FAM2]. Below I am quoting 'verbatim' parts of automatic translation (French to English) of postings made by late Joël Duval (ZEN):
-----
"In 1906, the [Zenith] design office conceived a caliber, reference number 68. Equipped with a large balance wheel, this 19-ligne (41.30 millimeter) movement aimed for ultimate precision. The engineers would have liked to make it a competition-winning machine. Unfortunately, Zenith's chronometer experts, tasked with preparing watches for international chronometry competitions, particularly those of the Neuchâtel Observatory, saw things differently and preferred to work on 20.5-ligne calibers, which were easier to regulate. Sandwiched between the so-called "Zenith" 18-28 caliber and the 20.5 ligne movement, this 19 ligne caliber was not immediately manufactured and remained in storage for nearly 40 years! Indeed, the manufacture only launched production of a small series of these high-end movements in 1943 under reference 69. A few watches were equipped with it, notably for export to North American markets. The movement was then shelved again, and it would be another 13 years before it was brought back into production.
....
It wasn't until the mid-1950s that Zenith decided to utilize its movement blanks after the Canadian Railways placed an order with the Le Locle manufacture. More precisely, at the end of 1955, Peter [
Kushnir], then Zenith's representative in Canada and who would become head of chronometry for the Canadian Railways in 1964, faced a shortage of movements for assembling the country's official railway watches. ... Peter Kushnir therefore requested that the manufacture modify the Calibre 69 to adapt it to the railway's specifications.
....
This movement, measuring 41.30 mm in diameter and 6.45 mm in height, is referenced as number 69 in the manufacture. It is of Extra quality with 21 jewels, Breguet regulation, and a regulator system. Featuring a Côtes de Genève finish, it has been regulated in six positions and temperatures and beats at 18,000 vibrations per hour. While the ébauches date from the first half of the 1940s, the movements were completed in 1956. ZENITH therefore put this RR56 into production...
ZENITH therefore did not opt for its patented eccentric disc regulator, introduced in 1903 and used by the manufacture until the 1960s. This 19-ligne movement is a 21-jewel movement made specifically for this exceptional order. Nicknamed " The Canadian " in the ZENITH workshops, the RR56, its name for distribution to the Canadian railways, is considered one of the manufacture's most aesthetically pleasing movements. The quality of its finishing certainly plays a significant role in this.
...
Zenith delivered 1,100 examples of its RR56 movement .... The manufacturer thus reserved a large portion of the manufactured movements either for after-sales service or, presumably, in anticipation of future orders, likely following an agreement that stipulated the outright exchange of calibers in case of retirement or failure.
....
The 68 movement, a close relative of the RR 56, reappeared later under the reference 68-21 in 1961, this time with 6,000 pieces delivered in 1961 and 1962, based on the 1943 movement blanks.
Including the RR 56 versions, a little over 7,000 pieces were distributed in total. The caliber 68[-21] has a smooth, rhodium-plated finish and is equipped with shock protection. Its counter-pivot plate with the anchor escapement is almost entirely in its original condition, barely adjusted on the edge of the mainplate. It features the same swan neck as the RR 56, but instead of the " Prima" designation assigned to the RR 56, the movement became "Extra Prima ," meaning the highest-end in Zenith's catalog.
...
Rather rare, this caliber 68-21, though easier to find than the RR56, shares with its sibling movement extreme precision and a distinctive architectural beauty.
---------
Above are but short snippets from the original
post. Please go check it out if at all interested; it has much more detail + photos. Thankfully nowadays at least Chrome and Safari have the automated translate button in the address bar (don't ask how is my French). Personally I found the translation through Chrome much better.
And lastly, here are photos of my watch (note that the dial has slight damage around 5; 52.4mm diameter, 109g, movement serial number I think is hiding under balance wheel, 0.800 silver outer case /w metal inner case, case n
😲 9678805). I am going to call beginners luck on this one!
[FAM1]
https://forumamontres.forumactif.com/t208957-zenith
[FAM2]
https://forumamontres.forumactif.com/t197540-zenith-de-poche-23-et-25-rubis
[NAWCC]
https://mb.nawcc.org/threads/zenith-extra-prima-21-jewels-calibre-68.177792/
[WUS]
https://www.watchuseek.com/threads/zenith-extra-prima-21-rubis.3508850/
[Kushnir]
https://www.ucc.ca/wp-content/uploads/2019/09/Peter-Kushnir-the-last-CPR-clockman-spoke-a-rare-‘horological’-dialect-The-Globe-and-Mail.pdf