Breguet MARINE ÉQUATION MARCHANTE 5887 Mode D'emploi page 28

4. Adjusting the month of the equation
E pushbutton II
English
Pushbutton II adjusts the month of the equation B'.
Use pushbutton II to adjust the month of the equation B' by
referring to the graduations on the sapphire disk up until the
month preceding the current month. The month of the equation
B' must be identical to the calendar month B.
In this example, the indicator is pointing to the beginning of the
month of December (D).