• circle chart;
  • periodicity;
  • outer control limit;
  • inner control limit;
  • process monitoring

Measurements with a periodicity are common in practice but there have been no specific monitoring control techniques for them. In this paper, we propose a type of control chart that plots measurements around a circle so that information from the same stage of different cycles can be readily compared. Some basic properties of such charts are investigated, and further developments are discussed. The basic circle chart can be applied under various kinds of control chart schemes, and there is potential for further development. Some application examples are also shown in this paper. Copyright © 2012 John Wiley & Sons, Ltd.