Looking at the shining bezel, hour markers, domed front dial and crystal, brushed case sidelines, 816.423 leaves an impression that has some kinds of connection to M177S. The overall workmanship of 816.423 is superb.
Based on the prototype of ST21, additional features like
the moon phase at 2 o’clock, power reserve indicator at 10 o’clock, date
sub-dial at 6 o’clock. make this watch appear more multi-functional and complicated,
while maintaining its advantage of 28800 high vibration per hour.