1. Ambro?, P.: 1992, in K. Harvey (ed.),The Solar Cycle, ASP Conference Series 27, 35.
2. Bevington, P. R.: 1969,Data Reduction and Error Analysis for the Physical Sciences, McGraw-Hill Inc., New York.
3. Bogart, R. S., Ferguson, S. H., Scherrer, P. H., Tarbell;, T. D., and Title, A. M.: 1988,Solar Phys. 116, 205.
4. Brandt, P. N., Ferguson, S., Scharmer, G. B., Shine, R. A., Tarbell, T. D., Title, A. M., and Topka, K.: 1991,Astron. Astrophys. 241, 219.
5. Chou, D.-Y., Chen, C.-S., Ou, K.-T., and Wang, C.-C.: 1992,Astrophys. J. 396, 333.