It's about thirty times as long as a Giant Tortoise's Lifespan.
In other words, the length of a Giant Tortoise's Lifespan is 0.029 times 839.3 decades.(for Adwaita, an Aldabra Giant Tortoise) (Dipsochelys dussumieri, formerly Geochelone gigantea)
It's about 90 times as long as Pepi II's reign.
In other words, the length of Pepi II's reign is 0.01 times 839.3 decades.(a.k.a. Neferkare) (2278 BCE - 2184 BCE)
It's about 250 times as long as Pius IX's reign.
In other words, 839.3 decades is 265.2 times the length of Pius IX's reign, and the length of Pius IX's reign is 0.003771 times that amount.(a.k.a. Pope Blessed Pius IX, a.k.a. Giovanni Maria Mastai-Ferretti) (1792-1878)
The longest reigning Pope in the Church's history, Pius IX reigned from June 16th, 1846 to February 7th, 1878 — 3.165 decades. As the last monarchical Pope, he ruled over 3,000,000 subjects in the Papal States until 1870.
It's about 700 times as long as FDR's Presidential Term.
In other words, 839.3 decades is 693.2 times the length of FDR's Presidential Term, and the length of FDR's Presidential Term is 0.001443 times that amount.(a.k.a. Franklin Roosevelt, a.k.a. Franklin Delano Roosevelt) (1933-45)
It's about 900 times as long as King Tut's reign.
In other words, the length of King Tut's reign is 0.001 times 839.3 decades.(a.k.a. Tutankhamun, a.k.a. Tutankhaten, a.k.a. tVwa:t-ʕa:nəx-ʔaˡma:n) (1333 BCE - 1324 BCE)
Pharaoh of the 18th dynasty, Tutankhamun begin his reign at the age of eight in 1333 BCE and remained pharaoh until 1324 BCE — 0.9 decades later. When artifacts from Tut's tomb were on display at the Metropolitan Museum of Art (New York City, New York) from late 1976 to 1979, they were viewed by an estimated 8 million people.
It's about 1,000 times as long as The Revolutionary War (American).
In other words, 839.3 decades is 1,002 times the length of The Revolutionary War (American), and the length of The Revolutionary War (American) is 0.000998 times that amount.(a.k.a. American War of Independence) (1775-83)
It's about 1,500 times as long as The Construction of the Chunnel.
In other words, 839.3 decades is 1,314 times the length of The Construction of the Chunnel, and the length of The Construction of the Chunnel is 0.000761 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.