It's about one-one-hundred-fiftieth as long as a Giant Tortoise's Lifespan
In other words, the length of a Giant Tortoise's Lifespan is 170 times 18 months.(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 3,000 months 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 2,300 months as a British colony.
It's about 200 times as long as The Great Chicago Fire
In other words, the length of The Great Chicago Fire is 0.005 times 18 months.(1871) (Chicago, Illinois)
The Great Chicago Fire started at about 9am and burned for 0.07 months between October 8th and October 10th, 1871. Chicago had experienced twenty smaller fires in the 0.50 months leading up to the blaze, due to drought conditions, strong winds, and the abundance of wooden buildings at the time.
It's about 400 times as long as The Battle of Fort Sumter
In other words, 18 months is 390 times the length of The Battle of Fort Sumter, and the length of The Battle of Fort Sumter is 0.0026 times that amount.(1861)
The first battle of the American Civil War, the Battle of Fort Sumter began with the shelling of the Fort at 4:30 am on April 12th, 1861 and concluded with the surrender of the Fort by its Commander Robert Anderson at about 1:30pm on April 13th, 0.045 months later. The Battle's only casualties were the accidental shootings of two Union soldiers during the surrender ceremony.
It's about 800 times as long as The First Transatlantic Flight (Alcock and Brown, 1919)
In other words, 18 months is 811 times the length of The First Transatlantic Flight (Alcock and Brown, 1919), and the length of The First Transatlantic Flight (Alcock and Brown, 1919) is 0.00123 times that amount.(John Alcock and Arthur Whitten Brown) (1919) (first non-stop flight)
In an effort to win a £10,000 prize from London's The Daily Mail, John Alcock and Arthur Brown completed a flight from St. John's, Newfoundland to Connemara, Ireland in 0.0222 months in June, 1919. In spite of their fame as aviators, Brown would never fly again after this trip and Alcock would lose his life during a flight to France less than six months later.
It's about 900 times as long as The First light bulb test (Edison, 1879)
In other words, 18 months is 906 times the length of The First light bulb test (Edison, 1879), and the length of The First light bulb test (Edison, 1879) is 0.0011 times that amount.(Thomas Edison's filament Thread No. 9) (1879) (total time)
Lit at 1:30am on October 22nd, 1879, the first Edison completed his first majorly successful test of his light bulb, which continued to burn for 0.0199 months until the bulb glass succumbed to the heat and cracked, extinguishing the filament. Within 36 months of his success, Edison was selling 45,000 light bulbs per day to large companies across the country.
It's about 1,500 times as long as The Longest Pro Baseball Game
In other words, 18 months is 1,560 times the length of The Longest Pro Baseball Game, and the length of The Longest Pro Baseball Game is 0.000641 times that amount.(1981) (McCoy Stadium, Pawtucket, Rhode Island)
The longest professional baseball game in history — a triple-A game between the Pawtucket Red Sox and the Rochester Red Wings — took place between April 18th and 19th, 1981 lasting a total of 0.0115 months (and 33 innings). The Red Sox ultimately won the game 3-2, but not before the game set twelve records, including the most plate appearances by a single player - a three-way tie between Tom Eaton, Dallas Williams, and future Hall-of-Famer Cal Ripken Jr., all of Rochester.
It's about 2,000 times as long as The First Indianapolis 500
In other words, 18 months is 1,960.60 times the length of The First Indianapolis 500, and the length of The First Indianapolis 500 is 0.00051005 times that amount.(a.k.a. Indy 500, a.k.a. International 500-Mile Sweepstakes Race) (1911) (Indianapolis, Indiana)
The first recorded automobile race of its distance, the inaugural Indianapolis 500 was won by Ray Harroun in 0.009181 months. Haroun's average speed through the race was 120 kph (74.59 mph).