Egyptologists have two other ways to find the total number of years. For the Old Kingdom, they can use the number of cattle censuses. For later periods, they can use the celebration of a sed festival. In the Old Kingdom, there was a regular census where the number of cattle was counted. At first this was believed to have taken place every two years. There were 24 cattle censuses during the rule of Sneferu, who therefore ruled for 48 years. However new research has shown the census was sometimes held every year, or at gaps of more than two years. The sed festival was held on the 30th anniversary of the Pharaoh's rule. A ruler with one sed festival recorded would have ruled at least 30 years. However, this may not be the usual practice in all cases.