code: public Number getSV()
     {
        Number variance = (Number) getCachedValue(AssignmentField.SV);
        if (variance == null)
        {
           Number bcwp = getBCWP();
           Number bcws = getBCWS();
           if (bcwp != null && bcws != null)
           {
              variance = NumberHelper.getDouble(bcwp.doubleValue() - bcws.doubleValue());
              set(AssignmentField.SV, variance);
           }
        }
        return (variance);
     }
docs: The SV (earned value schedule variance) field shows the difference in
  cost terms between the current progress and the baseline plan of the
  task up to the status date or today's date. You can use SV to
  check costs to determine whether tasks are on schedule.
  
  @return -earned value schedule variance