The V72.6 (or UG 130) it is based on the 72 (or UG cal 85).
The balance wheel is different and it uses a breguet hairspring. It beats 21000 alt / h instead of 19600, hour reset counter has a modified mechanism which is more reliable than that of standard V72. It formed the base movement for the 72.7 developed by Rolex in 6263 and 6265. Only 47K Valjoux 72.6 were manufactured while the V72 has been made him more than 260,000 copies. Therefore, a much better and rare movement than the V72 or caliber 85. That is why they are so difficult to find!
The caliber 85 replaced the caliber 130. It was cheaper to make but less reliable and of lower quality.
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