1. Altrock, R. C. (ed.): 1988, Proceedings of the Ninth Sacramento Peak Summer Symposium, National Solar Observatory, Sunspot, p. 414.
2. Babcock, H. W.: 1961, Astrophys. J. 133, 572.
3. Bao, K.: 1984, Publ. Beijing Astron. Obs. 5, 1.
4. Bao, K.: 1989, Publ. Beijing Astron. Obs. 12, 47.
5. Bevington, P. R.: 1969, Data Reduction and Final Analysis for the Physical Sciences, McGraw-Hill, New York, p. 73.