Thank you for the explanation, Alan.
Are the numbers on the dial just reminders of the FL-numbers, or is there a connection with using the hands of the watch and/or the bezel?
Martin,
I do not claim to be anywhere near a knowledgable pilot having less than 150 hours in my logbook. However I will answer your questions as best I can.
Please note that the way flight levels are set up varies in different countries and the following is a simplification based essentially on what I have observed on Breitling pilot's watches and what I have learnt about the system used in the US. I am not sure which country(ies) Breitlings with FLs are designed to be used in but it is not the UK. Here in the UK where I live we have a slightly different system of flight levels based on four directions of flight rather than just two as used in the US and on Breitling watches.
IMHO the FL numbers around the edge of the dial are reminders only and have no
direct connection with the time and no connection at all with the chronograph hands. And they also have no connection at all with the slide rule such as on a Navitimer ref 806.
However they
do have a simple connection with the compass degrees on a watch that has a windrose bezel (for those unfamiliar with the term "windrose" it means a bezel marked in compass directions rather than the more common countdown or countup bezel marked in minutes or hours). If the windrose bezel is set with 0 degrees (ie due north) pointing towards 12 o'clock, any magnetic heading towards the right side of the bezel (and including 0 degrees) should be undertaken at one of the flight levels marked on the right side of the dial. And any magnetic heading towards the left side of the bezel (and including 180 degrees) should be undertaken at one of the flight levels marked on the left side of the dial.
This is clearly illustrated on the Breitling Hercules which has a windrose bezel and flight levels marked on the dial:
On the Hercules the red FLs are for VFR flight and the black for IFR flight. As I say, this is very simple in concept and once known does not require much grey matter to get right!
Additionally, in terms of your question about whether there is any connection between flight levels and the bezel, it seems to me that if a watch with a windrose bezel is being used as a solar compass (now indeed using the watch hands, to find due south and then align the bezel with it), one could then read off one's track (need to allow for magnetic variation and any cross-wind component but I'll ignore those for the purposes of this explanation) and then easily see the available flight levels. Naturally, great care is needed when close to a course of 0 degrees or 180 degrees!
Although this no doubt seems very simple in concept, when under high workload in the cockpit anything that simplifies, and importantly reduces the possibility of error, is not merely helpful but can be lifesaving.

I must admit that I am a little concerned that what I have just written may only be intelligible to someone who already knows all about this - my apologies if my writing style has rendered it non-understandable!
Cheers,