In response to the discussion about the Caliber 11-I, with the special marking on the back of one of the lugs, let me present the following excerpt, taken from a draft of Part 3 of my series about the Chronomatics / Caliber 12 chronographs.

I hope that you find this information interesting and useful, as you seek to determine whether you have a Caliber 11 or a Caliber 11-I. Thanks to David for raising this issue; thanks to Hans for providing most of the following information.

Now, let's see who can show us some Caliber 11-I chronographs!!

Jeff

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Caliber 11 -- The Early Problems

The Caliber 11 movement was plagued with technical problems, from the beginning. Some of these technical problems arose from decisions made in designing the watches; others arose from poor engineering or a lack of development of the movement, as the Chronomatic group competed to bring the first automatic chronograph onto the market. The following were among the most significant "technical" problems with the original Caliber 11 chronographs:

• While most chronographs of the period utilized a “jumping” minute recorder and a “creeping” hour recorder, the Caliber 11 used a jumping hour recorder as well as a jumping minute recorder. The needles on the chronograph "jumped" every 30 minutes (and every minute), rather than moving continuously. Having the needle "jump" required incrementally more power than having them creep on a continuous basis.

• The Caliber 11 was also designed so that the date disk would "jump" in a relatively short period of time (beginning at 11:45 p.m.), rather than beginning to change earlier in the evening (for example, at 10:30 p.m.). This jumping date disk also required incrementally more power than a disk that would move more gradually over the course of a longer period.

• In order to provide the power that would be required to power the watch, with the chronograph running, the needles jumping, and the hour disk changing within a relatively short period of time, the Caliber 11 required a strong mainspring. The mainspring used for the Caliber 11 turned out to be too strong, resulting in the problem of "banking" (or “rebanking”), meaning that the balance wheel had too much amplitude and caused the watch to run too fast.

• Finally, the Caliber 11 movement had problems with its oscillating pinions, which had a brass head on a steel shaft. This brass head turned a brass wheel (Number 8000), and both these parts wore out too quickly.

The Caliber 11-I Movement

As a result of these technical problems with the Caliber 11 movement, within a year of its introduction, the Chronomatic group (Hueer-Breitling-Hamilton) made the changes that resulted in the creation of the Caliber 11-I movement. (We are not certain, but can assume that the "I" designation indicated that the movement had been "Improved".) Changes from the original Caliber 11 to the improved Caliber 11-I included the following:

• changes in the mainspring and balance wheel, to address the problem of "banking"

• the date advance wheel (jumper) was slowed, so that the date began to change at 10:30 p.m. and occurred over the next 90 minutes

• the jumper springs on the minute and hour recorders were changed, so that less power was required for the needles to jump each minute and each 30 minutes.

• the oscillating pinion was changed from being bi-metallic (steel and brass) to solid steel, and the chronograph runner wheel (8000) was made of a nickel-silver alloy, rather than brass

A collector can confirm that his Heuer chronograph is powered by the Caliber 11-I movement, by checking for two special marks. The main chronograph bridge will be marked with the usual "11", but there will be a small "I" under the balance wheel. In addition, the case of any chronograph that used the Caliber 11-I movement was marked with a small star (*) on the back of one of the four lugs. In addition, the color of the barrel changed from rose color in the Caliber 11 to nickel-plated in the Caliber 11-I. Finally, whereas the date change on the the Caliber 11 began shortly before midnight (at around 11:45), the date change on the Caliber 11-I will begin much earlier, at around 10:30.

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In the following photo, notice the small "I", at the very bottom, below the balance wheel, indicating that this is an "Improved" (or modified) Caliber 11 movement.