Sources contemporary to Khufu's time give three key pieces of information: One of them was found at the Dakhla Oasis in the Libyan Desert. Khufu's serekh name is carved in a rock inscription reporting the ""Mefat"-travelling in the year after the 13th cattle count under Hor-Medjedu". The second source can be found in the relieving chambers inside Khufu's pyramid above the burial chamber. One of these inscriptions according to Flinders Petrie mentions a workmen's crew named "friends of Khufu" alongside the note "in the year of the 17th cattle count", but it is questioned if the number of years points to a biennial cattle count, or if the number must be taken verbatim. Though Zahi Hawass has reported locating the inscription of the date given by Petrie, there is also some debate whether Petrie may have mistakenly relied on other sources as the inscription has otherwise yet to be found. Newer evidence from Wadi al-Jarf however, gives a third clue about the true length of reign: Several papyrus fragments contain handwritten reports from a royal harbour at modern-day Wadi al-Jarf. The inscriptions describe the arrival of royal boats with precious ore and turquoise in the "year after the 13th cattle count under Hor-Medjedw". Therefore, Khufu's highest known and certain preserved date is the "Year after the 13th cattle count".