It's about nine-tenths as long as Pepi II's reign.
In other words, the length of Pepi II's reign is 1 times 9 decades.(a.k.a. Neferkare) (2278 BCE - 2184 BCE)
It's about one-third as long as a Giant Tortoise's Lifespan.
In other words, the length of a Giant Tortoise's Lifespan is 2.8 times 9 decades.(for Adwaita, an Aldabra Giant Tortoise) (Dipsochelys dussumieri, formerly Geochelone gigantea)
It's about three times as long as Pius IX's reign.
In other words, 9 decades is 2.844 times the length of Pius IX's reign, and the length of Pius IX's reign is 0.3516 times that amount.(a.k.a. Pope Blessed Pius IX, a.k.a. Giovanni Maria Mastai-Ferretti) (1792-1878)
It's about seven-and-a-half times as long as FDR's Presidential Term.
In other words, 9 decades is 7.433 times the length of FDR's Presidential Term, and the length of FDR's Presidential Term is 0.1345 times that amount.(a.k.a. Franklin Roosevelt, a.k.a. Franklin Delano Roosevelt) (1933-45)
It's about nine times as long as King Tut's reign.
In other words, the length of King Tut's reign is 0.1 times 9 decades.(a.k.a. Tutankhamun, a.k.a. Tutankhaten, a.k.a. tVwa:t-ʕa:nəx-ʔaˡma:n) (1333 BCE - 1324 BCE)
It's about ten-and-a-half times as long as The Revolutionary War (American).
In other words, 9 decades is 10.74 times the length of The Revolutionary War (American), and the length of The Revolutionary War (American) is 0.09311 times that amount.(a.k.a. American War of Independence) (1775-83)
It's about fourteen times as long as The Construction of the Chunnel.
In other words, 9 decades is 14.09 times the length of The Construction of the Chunnel, and the length of The Construction of the Chunnel is 0.07097 times that amount.(a.k.a. Channel Tunnel, a.k.a. Le tunnel sous la Manche) (1987 thru 1994) (Folkstone, Kent, UK to Coquelles, Pas-de-Calais, France)
The construction crew of the Chunnel broke ground in England on December 15th, 1987 and the tunnel was inaugurated by the Queen of England and the President of France on May 6th, 1994 — a total construction time of 0.6382 decades. The 4.9 million cubic meters of chalk excavated from the UK side of the Chunnel was dumped within sea walls to create the 299,467.38 sq. km (74 acre) Samphire Hoe County Park near Dover, Kent.