code: public Duration getStartVariance()
     {
        Duration variance = (Duration) getCachedValue(AssignmentField.START_VARIANCE);
        if (variance == null)
        {
           TimeUnit format = getParentFile().getProjectProperties().getDefaultDurationUnits();
           variance = DateHelper.getVariance(getTask(), getBaselineStart(), getStart(), format);
           set(AssignmentField.START_VARIANCE, variance);
        }
        return (variance);
     }
docs: Calculate the start variance.
  
  @return start variance