org.linkedin.util-core/src/main/java/org/linkedin/util/clock/Timespan.java
public Timespan add(Timespan other)
  {
    if(getTimeUnit() == other.getTimeUnit())
      return new Timespan(getDuration() + other.getDuration(), getTimeUnit());

    return new Timespan(getDurationInMilliseconds() + other.getDurationInMilliseconds(),
                        TimeUnit.MILLISECOND);
  }
public Timespan add(Timespan other)
  {
    if(getTimeUnit() == other.getTimeUnit())
      return new Timespan(getDuration() + other.getDuration(), getTimeUnit());

    return new Timespan(getDurationInMilliseconds() + other.getDurationInMilliseconds(),
                        TimeUnit.MILLISECOND);
  }
Adds another timespan to this timespan and return a brand new one. Note that the unit is
preserved if <code>other</code> has the same unit as 'this'.

@param other the timespan to add
@return a brand new timespan.