  Results of analysis of 60010 data photometric observations from the AAVSO
international database are presented, which span 120 years of monitoring. The
periodogram analysis shows the best fit period of 70.74d, a half of typically
published periods for smaller intervals. Contrary to expectation for
deep/shallow minima, the changes between them are not so regular. There may be
series of deep (or shallow) minima without alternations. There may be two
acting periods of 138.5 days and 70.74, so the beat modulation may be expected.
The dependence of the phases of deep minima argue for two alternating periods
with a characteristic life-time of a mode of 30years. These phenomenological
results better explain the variability than the model of chaos.
