1. d'Azambuja, L.: 1947, Quart. Bull. on Solar Activity, No. 77.
2. Fisher, R. R.: 1973, Sacramento Peak Obs., AFCRL-TR-73-0696, No. 205.
3. Rybanský, M., Ru?in, V., and Dzif?áková, E.: 1990, Bull. Astron. Inst. Czech. 41, 79.
4. Smartt, R. N.: 1982, SPIE, Vol. 331, Instrumentation in Astronomy IV, p. 442.