Form movements are nothing spectacular. Form movement with date indication are already pretty rare, and when you restrict it to ladies’ size, there’s not much to find.
One of the rare ladies’ watches form movements with date indication is the Otero 251, which bases on the Otero 25 and adds a simple calendar mechanism on top. With its nominal size of 5 1⁄4 lignes (17.4 x 19.9mm) it is a really tiny movement.
You see on the base plate, that all bearings, except those of the minute wheel, are equipped with rubies. You also see the stocky multi-storey construction, on which the bearing of the fourth wheel are above the escapement wheel.
The gear train consists of a large directly driven center minute wheel, followed by two tiny wheels, the third and fourth wheel, and finally the escapement wheel. It’s hardly possible to construct an even smaller gear train.
On the side view, the tiny gear train is even more impressive.
The Otero 251 has got a screw balance, which is beared in two Monorex shock protections. It beats contemporarily slow with 18000 A/h and can be adjusted by a long regulator arm. The escapement is a conventional swiss pallet lever escapement.
Without calendar module, the dial side is almost identical to that of the Otero 25, the only difference are two sleeves at the outer edges at 11:30 and 5:30 o’clock which fix the calendar module (which is mounted with two screws at 6:30 and 1:30 o’clock) and the double hour wheel, which drives the calendar mechanism.
The Otero 251 has got a rocking bar winding system and a ratchet on the dial side, which is very well made with a true ratchet.
The construction of the date indication is pretty simple: The hour wheel drives the switching wheel at 12 o’clock which rotates once a day and which has got a finger on its inner side, which advances the date disc. The spring at 9 o’clock ensures, that the date wheel locks properly. By turning the time backwards and fourth between 9 pm and 1am, the date can be corrected semi-fast.
The calendar module is mounted onto the dial side of the movement with the two well visuable screws.
Since the date is pretty small, there’s a tiny loupe in the crystal.
|Number of jewels:||17|
Nickel screw balance|
|Balance bearing / direction hairspring:||Clockwise|
|Adjust mechanism:||Long regulator arm|
|Construction type:||solid construction|
|Winding mechanism:||rocking bar winding system|
|Setting lever spring:||1 hole(s)|
|Functions:||hour, minute, day|
|Size:||5 1/4''' (measured: 17,4 x 19,9mm)|
Flume: 1962 29|