First number=Year of manufacture, Second and third numbers=Week of manufacture, Fourth number=Day of manufacture.
This code is often followed by a letter P. This simply indicates that the watch was made in Gretchen on the main production line near Biel.
Don.....
PS: Some watches are stamped with the letter P.The letter P ( not to be confused with the one following the date code) means that the watch was sold to a member of staff working in the factories (Personal edition).