cdm/src/main/java/ucar/nc2/time/CalendarDateUnit.java
public CalendarDate makeCalendarDate(double value) {
    if (isCalendarField)
      return baseDate.add(CalendarPeriod.of( (int) value, periodField));  // LOOK int vs double
    else
      return baseDate.add( value, periodField);
  }
public CalendarDate makeCalendarDate(double value) {
    if (isCalendarField)
      return baseDate.add(CalendarPeriod.of( (int) value, periodField));  // LOOK int vs double
    else
      return baseDate.add( value, periodField);
  }
inverse of makeOffsetFromRefDate