It's about two-fifths as long as King Tut's reign
In other words, 3.990 years is 0.4 times the length of King Tut's reign, and the length of King Tut's reign is 3 times that amount.(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 — 9 years 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 one-third as long as FDR's Presidential Term
In other words, 3.990 years is 0.3295 times the length of FDR's Presidential Term, and the length of FDR's Presidential Term is 3.04 times that amount.(a.k.a. Franklin Roosevelt, a.k.a. Franklin Delano Roosevelt) (1933-45)
FDR, the 32nd President of the United States, served from March 4th, 1933 to April 12th, 1945, dying after 12.110 years in office. At the time of his sudden death, Elizabeth Shoumatoff was painting a portrait of Roosevelt which, never finished, now hangs in a museum at the site of Roosevelt's Presidential retreat in Georgia.
It's about one-tenth as long as Pius IX's reign
In other words, 3.990 years is 0.1261 times the length of Pius IX's reign, and the length of Pius IX's reign is 7.93 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 — 31.650 years. As the last monarchical Pope, he ruled over 3,000,000 subjects in the Papal States until 1870.
It's about thirteen times as long as The First artificial heart patient's survival
In other words, 3.990 years is 13 times the length of The First artificial heart patient's survival, and the length of The First artificial heart patient's survival is 0.077 times that amount.(1982) (Dr. Barney Bailey Clark; first permanent, pneumatic device)
On December 2nd, 1982 Dr. William DeVries implanted the first artificial heart into Dr. Barney Bailey Clark, who went on to live for 0.3070 years. This early model of the artificial heart was controlled and powered by an external, 146.51 kg (323 lb) machine that Dr. Clark had to cart with him as he moved throughout the hospital.
It's about thirteen-and-a-half times as long as The Spanish-American War
In other words, 3.990 years is 13.4 times the length of The Spanish-American War, and the length of The Spanish-American War is 0.075 times that amount.(1898)
The War between Spain and the United States over the liberation of Cuba began on April 25th, 1898 and lasted until the signing of the Treaty of Paris on August 12th, 1898, 0.2960 years. The Treaty gave the United States control of Cuba, the Philippines, Puerto Rico, and Guam.
It's about sixteen times as long as The First spaceflight (Sputnik)
In other words, 3.990 years is 16 times the length of The First spaceflight (Sputnik), and the length of The First spaceflight (Sputnik) is 0.06 times that amount.(a.k.a. Sputnik 1, a.k.a. Спутник-1, a.k.a. "Satellite-1", a.k.a. Простейший Спутник-1) (1957) (total time in orbit)
Launched from Kazakhstan in 1957, Sputnik was the first artificial satellite placed into orbit around Earth, where it remained for 0.250 years. During its voyage, it traveled about 70,000,000 km (43,495,983.46 mi), completing an orbit of the planet every 0.00018 years.
It's about twenty times as long as Columbus' voyage to America
In other words, 3.990 years is 20 times the length of Columbus' voyage to America, and the length of Columbus' voyage to America is 0.1 times that amount.(1492) (first voyage)
Attempting to find a western route to Asia, Christopher Columbus set sail on August 3rd, 1492 and landed in the Bahamas on October 12th — 0.20 years later. After one of Columbus' ships, the Santa Maria ran aground in present-day Haiti, he ordered that the timber be used to used to build a fort and settlement called La Navidad; it remains missing to archaeologists to this day.