The Jeambrun 23D, a handwound movement of the fifties, which was used quite often, originates from France, from the village of Maîche of the departement Doubs near the northwest swiss border.
It was available in several versions, which differed by their decoration, the number of used jewels and shock protection systems.
All in common is the unusual construction, where the mainspring barrel is located at "6" and the balance is located at "12". Hence the barrel arbour wheel is located to the right of the crown wheel and not, as usual, at the left.
The golden toned Glucydur screw balance was beared in different shock protection systems, such as Incabloc, Ruby-Shock and others.
The hairspring is fix mounted at the balance cock and can be regulated in its effective length with the help of a long regulator arm. This helps slower beating watches (with 18000 A/h) to achive good timing results.
The train construction is pretty modern with its directly driven center second indication.
The minute wheel is located under an own bridge - pretty modern for the fifties. For a perfect bearing of the concentric second wheel, a loose(!) ruby was put onto the bridge.
Of course, all bearings, except the mainspring barrel bearing, contain synthetic rubis. It the more elaborate version, even 6 of them have got cap jewels on their top. More functional rubis are hardly possible.
On the dial side, you see the yoke winding system with its characteristic setting lever spring, which contains only two holes.
As usual on those old movements, the Jeambrun 23D contains a helping minute scale, which can be used for timing the watch without timegrapher.