grib/src/main/java/ucar/nc2/grib/grib1/Grib1SectionProductDefinition.java
public final CalendarDate getReferenceDate() {
    int century = getReferenceCentury() - 1;
    if (century == -1) century = 20;

    int year = getOctet(13);
    int month = getOctet(14);
    int day = getOctet(15);
    int hour = getOctet(16);
    int minute = getOctet(17);
    return CalendarDate.of(null, century * 100 + year, month, day, hour, minute, 0);
  }
public final CalendarDate getReferenceDate() {
    int century = getReferenceCentury() - 1;
    if (century == -1) century = 20;

    int year = getOctet(13);
    int month = getOctet(14);
    int day = getOctet(15);
    int hour = getOctet(16);
    int minute = getOctet(17);
    return CalendarDate.of(null, century * 100 + year, month, day, hour, minute, 0);
  }
Reference Date (octet 13-17).
Reference time of data – date and time of start of averaging or accumulation period.

@return Reference Date as CalendarDate.