The calibre 11 was the first automatic chronograph movement when it was revealed to the market in 1969 in the first 1133 Monaco. Because of the rush to be first to market with Heuers partners this groundbreaking movement needed some improvements shortly after release and in 1970 the calibre 11i was released fine tuning the movement. The calibre 11i was the mainstay movement of the Heuer Monaco 1133 range.
The calibre 15 movement was introduced in 1972 when the need for a cheaper movement came about due to the competitive watch marketplace. This movement made it into the 1533 Monaco and made do without the 12 hour register, but with a perpetual second hand at 10oclock giving the calibre 15 watches their unique look. The movment also used some cheaper parts which allowed Heuer to reduce the retail price by 10%.
The calibre 12 movement improved further on the 11i and was introduced during the 1133 Monacos lifecycle in 1971. you will find some 1133 variants came with calibre 12 movements as standard and some would have replaced faulty calibre 11 movements during Heuer service work. The main improvements were strengthening of some key parts and a faster beat rate from 19800 VPH to 21600 VPH