The history of El Primero accelerated about 1967 when the rumour swelled of a competitor project led by Breitling, Hamilton-Büren, Heuer and Dubois-Depraz. Without being able to date it precisely, it is probable that the objective of a functioning caliber with 36, 000 vibrations per hour was not in the initial specifications and that it is under development that the engineers of ZENITH for some, come from other houses which had given up this technology, imported this idea at ZENITH.
The main competition of Movado/ Zenith came from the amalgamation of the chronograph specialists Breitling and Heuer-Leonidas with Hamiliton-Bruen and Dubois Depraz, who started the development of their project in 1965. When the delegation of the four houses met together for the first time in 1965, they were so obsessed with keeping things quiet that they gave their project a confidential code name: 99. During this meeting, the role each house would play was distributed in utter secrecy. Bruen would be in charge of the special automatic mechanism (adapted from Bruen’s "Intramatic" Caliber : Planetary rotor of heavy winding in both direction via gliding pinion); Dubois-Depraz would be responsible for the chronographic module (chronograph unit 8510 with coulisse-lever switching, equipped with a 12-hour and a 30-minute counter) as well as the oscillating pinion invented by Edouard Heuer. Breitling and Heuer would develop the other components and oversee the design of the watch dial and case.
περα απο αυτο τον χρονογραφικο μηχανισμο δεν τον εφτιαξε η heuer αλλα οι αλλες δυο του γκρουπ,εγω γνωριζω οτι ηταν ο πρωτος αυτοματος της Zenith