Description
Mechanical chronograph movement, stopwatch function with hours, minutes and seconds, hour and minute counters combined in a totalizer at 12 o'clock, flyback function, small hacking seconds, perpetual calendar, large double-digit display for both the date and month, leap year display.
All watches using this caliber:

IW3972-02 IWC Portugieser Perpetual Calendar Digital Date-Month Edition "75th Anniversary" Red Gold / Black

IW3972-03 IWC Portugieser Perpetual Calendar Digital Date-Month Edition "75th Anniversary" Red Gold / Silver