code: private function getNewSince ($channelId, $limit, $before = null)
  	{
  		$db = Neuron_DB_Database::getInstance ();
  
  		$where = "TRUE";
  		if (isset ($before))
  		{
  			$where = "c_m_id < " . intval ($before);
  		}
  
  		$limit ++;
  
  		$sql = "
  			SELECT
  				c_m_id
  			FROM
  				n_chat_messages
  			WHERE
  				c_c_id = '{$channelId}' AND
  				{$where}
  			ORDER BY
  				c_m_id DESC
  			LIMIT
  				{$limit}
  		";
  
  		$messages = $db->query ($sql);
  
  		$count = count ($messages);
  		if ($count > 0)
  		{
  			// minus one, because we need to get the first
  			// message as well. This might result in showing
  			// 21 messages, but that's okay.
  			return $messages[$count - 1]['c_m_id'] - 1;
  		}
  		return null;
  	}
docs: Return the $since id that is $amount messages ago.