Not knowing whether monarchies were simultaneous or sequential results in widely differing chronological interpretations.
Where the total number of regnal years for a given ruler is not known, Egyptologists have identified two indicators to provide that total number: for the Old Kingdom, the number of cattle censuses; and for later periods, the celebration of a sed festival.
The sed festival was usually celebrated on the thirtieth anniversary of the Pharaoh's ascension, thus rulers who recorded recording one could be assumed to have ruled at least 30 years.
However, once again, this may not be the usual practice in all cases.
Her television crew filmed and took pictures of at least 25 half-naked men as they were arrested for "perversion" and dragged into police trucks.