In 1964, when Heuer and Leonidas merged the 3-6-9-12 Master-Time received a new movement: Arogno cal. 28H instead of Revue-Thommen cal. 63 and this movement was stamped Heuer-Leonidas S.A. At the same time to that the new 12h MT was launched, but the with the 13mm case, too. Until 1967 the case of both MT remained with 13mm height. 1967 the new line of Monte-Carlo was launched and the case height increased from 13mm to 15mm. This had an impact on the Master-Time, especially for the pair of them in the Rallye-Master. From 1967 on the 12h MT had also the 15mm case.

Conclusion & question:

Obviously the 3-6-9-12 Master-Time was still built during this period just to meet the 3-button Monte-Carlo for the Rallye-Master. Is it possible, that the 12h Master-Time with the 13mm case was then also paired with the 3-button Monte-Carlo for the RM?