It's about twenty times as long as The Voyage of the Mayflower
In other words, 3.990 years is 22 times the length of The Voyage of the Mayflower, and the length of The Voyage of the Mayflower is 0.05 times that amount.(1620)
Having left Southampton, England on September 16th (new style), 1620, the Mayflower dropped anchor near Cape Cod, Massachusetts 0.180 years later on November 21st (new style), 1620. The voyagers had planned to travel in a convoy of two ships, but the smaller Speedwell was found to be leaking (evidently as a result of sabotage) and all passengers had to be moved to the Mayflower instead.
It's about one-twenty-fifth as long as Pepi II's reign
In other words, 3.990 years is 0.0 times the length of Pepi II's reign, and the length of Pepi II's reign is 30 times that amount.(a.k.a. Neferkare) (2278 BCE - 2184 BCE)
The sixth dynasty pharaoh of Egypt's Old Kingdom, Pepi II Neferkare ascended to the throne at the age of six and is generally thought to have reigned until his death at the age of one-hundred — a total of 94 years. His reign was the longest of any monarch in history.
It's about thirty times as long as The First US Continental Congress
In other words, 3.990 years is 29 times the length of The First US Continental Congress, and the length of The First US Continental Congress is 0.03 times that amount.(1774) (Philadelphia, Pennsylvania)
The First Continental Congress — which included such notable members as Samuel Adams, Thomas Paine, Patrick Henry, John Jay and George Washington — met from September 5th to October 26th, 1774 — a total of 0.140 years. Of the thirteen original American colonies in existence at the time, only the Province of Georgia sent no delegates to the Congress.
It's about 45 times as long as a William Henry Harrison's Presidency
In other words, 3.990 years is 46.24 times the length of a William Henry Harrison's Presidency, and the length of a William Henry Harrison's Presidency is 0.0216 times that amount.(a.k.a. William Henry Harrison, a.k.a. "Tippecanoe," a.k.a. "Old Tippecanoe") (1841)
Having caught pneumonia and pleurisy early in his term as President of the United States, William Henry Harrison died after 0.0863 years minutes in office. Following his death, Congress approved a Presidential widow's pension for Harrison's wife, Anna Symmes, who received a year's worth of Harrison's presidential salary — $25,000 — and the right to free postage for the remainder of her life.
It's about one-sixty-fifth as long as a Giant Tortoise's Lifespan
In other words, 3.990 years is 0.02 times the length of a Giant Tortoise's Lifespan, and the length of a Giant Tortoise's Lifespan is 63 times that amount.(for Adwaita, an Aldabra Giant Tortoise) (Dipsochelys dussumieri, formerly Geochelone gigantea)
Adwaita, an Aldabra Giant Tortoise who lived the later part of his life in the Alipore Zoological Gardens in Kolkata, India, was 250 years old at the time of his death. Once a pet of Major-General Robert Clive, 1st Baron Clive, who is credited with securing India as a colony of Great Britain, Adwaita lived through the entirety of India's 190 years as a British colony.
It's about 95 times as long as Boniface VI's reign
In other words, 3.990 years is 97 times the length of Boniface VI's reign, and the length of Boniface VI's reign is 0.0 times that amount.(AD 896)
The Church's enigmatic, shortest-reigning Pope, Boniface VI was pontiff for a period of 0.041 years in AD 896 before dying under somewhat mysterious circumstances. His election was subsequently pronounced null by Pope John IX because Boniface had been previously defrocked while serving as a Roman priest.
It's about 200 times as long as The Apollo 11 Mission
In other words, 3.990 years is 179.08 times the length of The Apollo 11 Mission, and the length of The Apollo 11 Mission is 0.0055841 times that amount.(1969) (total mission length)
The first trip by humans to the surface of the Moon, the Apollo 11 Mission began with the launch of the spacecraft from the Kennedy Space Center in Florida on July 16th, 1969 and concluded with the return of the command module on July 24th, 1969 — a total mission time of 0.0222804 years. The total time spent by astronauts Neil Armstrong and Edwin "Buzz" Aldrin on the Moon's surface was 0.000297868 years.