At the First International Conference on Comet Hale-Bopp (Canaries, 1998) many astronomers agreed with the value of the period of axial rotation of its nucleus, which was obtained by observers by a comparison of the two sequential patterns of the dust arcs. It was noted that the pattern had been repeated each ~12 hours. The value 11.35 h was taken as the period of axial rotation. However, alternative periods of 4 and 8 days have also been suggested. The possible reasons for this discrepancy are discussed. It is shown that a short period could be obtained by a misidentification of the same arc on two sequential images and, as a result, an overestimate of the radial velocity of dust in the arcs. To obtain the half day period one must take the projected velocity of the arc ~ 1.6 km/s, which exceeds the H2O gas expansion velocity. If one takes a lower expansion velocity a longer period would be obtained.