It's about as long as The Construction of the Chunnel
In other words, 0.63820 decades is 0.999 times the length of The Construction of the Chunnel, and the length of The Construction of the Chunnel is 1.00 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 0.63820 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.
It's about one-and-one-tenth times as long as World War II
In other words, 0.63820 decades is 1.06 times the length of World War II, and the length of World War II is 0.9407 times that amount.(a.k.a. Second World War, a.k.a. WWII, a.k.a. WW2) (1939 - 1945)
The most widespread war in history, the Second World War is generally considered to have started with the German invasion of Poland on September 1st, 1939 and to have until the surrender of Japan on September 2nd, 1945, a total of 0.60040 decades. Also the deadliest conflict in history, the war had an estimated 60 million casualties globally.
It's about three-fourths as long as The Revolutionary War (American)
In other words, 0.63820 decades is 0.7617 times the length of The Revolutionary War (American), and the length of The Revolutionary War (American) is 1.313 times that amount.(a.k.a. American War of Independence) (1775-83)
The War between Great Britain and the its thirteen colonies in North America (now the United States) for the independence of the United States is generally considered to have started with the Battle of Lexington and Concord on April 18th, 1775 (sometimes known as "The Shot Heard 'round the World") and to have concluded with the signing of the Treaty of Paris on September 3rd, 1783 — 0.83780 decades. A total of 25,000 Americans are estimated to have died as a result of the war.
It's about seven-tenths as long as King Tut's reign
In other words, 0.63820 decades is 0.7 times the length of King Tut's reign, and the length of King Tut's reign is 1 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 — 0.90 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 one-and-a-half times as long as World War I
In other words, 0.63820 decades is 1.46 times the length of World War I, and the length of World War I is 0.685 times that amount.(a.k.a. First World War, a.k.a. Great War, a.k.a. World War, a.k.a. War to End All Wars, a.k.a. WWI, a.k.a. WW1) (1914 - 1918)
World War I is considered to have begun with the assassination of Austrian Archduke Franz Ferdinand on June 28th, 1914 and to have lasted until the signing of the armistice with Germany on November 11th, 1918, for a total of 0.4370 decades. However, the Treaty of Versailles which ended conflicts between the major powers was not signed until June 28th, 1919 and the last formal peace treaties were not signed until August 23rd, 1923 — 0.4780 decades after the armistice was signed.
It's about one-and-a-half times as long as The First walk around the world
In other words, 0.63820 decades is 1.486 times the length of The First walk around the world, and the length of The First walk around the world is 0.6729 times that amount.(1970 - 1974) (Dave, John, and Peter Kunst) (including time in recovery)
On June 20th, 1970, Dave Kunst set out from Waseca, Minnesota with $1,000 and a mule. Kunst completed his walk around the world (with a 0.03331 decades pause following an assault he suffered during the journey) on October 5th, 1974 — 0.42930 decades.
It's about one-and-three-fifths times as long as The Civil War (American)
In other words, 0.63820 decades is 1.6 times the length of The Civil War (American), and the length of The Civil War (American) is 0.625 times that amount.(a.k.a. War Between the States, a.k.a. the Great Rebellion, a.k.a. the War of the Rebellion) (1861-65) (United States)
The deadliest war in American history, the American Civil War is generally considered to have begun on with the attack on Fort Sumter on April 12th, 1861 and to have lasted until the surrender of Robert E. Lee's army on April 9th, 1865 — 0.3990 decades. A total of 620,000 American (including Confederate) soldiers are estimated to have lost their lives due to the war.