IBM i date converter

A 7-digit numeric field whose first digit is the century: 0 for 1900, 1 for 2000. It was born to fit a date into very little space and cross the millennium without ambiguity, once two digits for the year were no longer enough. It costs one byte more than YYMMDD and saves one against YYYYMMDD: a trade-off still sitting inside a great many production files. Watch out for six digits: 260727 can be either YYMMDD or Julian CYYDDD, and only the file layout can tell you for sure.