grib/src/main/java/ucar/nc2/grib/coord/TimeCoordIntvDateValue.java
public TimeCoordIntvValue convertReferenceDate(CalendarDate refDate, CalendarPeriod timeUnit) {
    if (timeUnit == null) {
      throw new IllegalArgumentException("null time unit");
    }
    int startOffset = timeUnit.getOffset(refDate, start);   // LOOK wrong - not dealing with value ??
    int endOffset = timeUnit.getOffset(refDate, end);
    return new TimeCoordIntvValue(startOffset, endOffset);
  }
public TimeCoordIntvValue convertReferenceDate(CalendarDate refDate, CalendarPeriod timeUnit) {
    if (timeUnit == null) {
      throw new IllegalArgumentException("null time unit");
    }
    int startOffset = timeUnit.getOffset(refDate, start);   // LOOK wrong - not dealing with value ??
    int endOffset = timeUnit.getOffset(refDate, end);
    return new TimeCoordIntvValue(startOffset, endOffset);
  }
Calculate the offset in units of timeUnit from the given reference date?