public function getBaseValue($unitId, $value)
{
$criteria = new \CDbCriteria();
$criteria->select = array('base_value');
$criteria->condition = 'unit_id = :unit_id AND value = :value';
$criteria->params = array(':unit_id' => $unitId, ':value' => $value);
$baseValue = self::model()->find($criteria);
return $baseValue->base_value;
}