Fallout’s nuclear rule of thumb theory is an innovative addition to Amazon’s TV adaptation of the beloved video game based on an antiquated protocol.

The rule of thumb seen in Amazon’s television adaptation of Fallout is a unique way of determining the impact of a nuclear explosion. Since the highly-anticipated series was released on Amazon Prime Video on April 10, 1014, Fallout has quickly emerged as one of the best series of the year. Fallout’s cast is led by a nearly unrecognizable Walton Goggins who plays Cooper Howard before he becomes The Ghoul, as well as Ella Purnell (Yellowjackets, Kick-Ass 2) as protagonist Lucy MacLean. Fallout’s stellar reviews have already led Amazon to renew the critically acclaimed series for a second season.

Although there are several changes that Amazon’s television adaptation of Fallout makes to the original game, the series does a magnificent job at keeping the core elements and themes alive despite its somewhat tricky content. This faithful adaptation led to many video game Easter eggs in the Fallout series, making the show even more exciting for devoted fans of the game while still being accessible to viewers who have never played the acclaimed games before. In what could be considered her breakout performance, Purnell shines alongside Goggin’s Ghoul character, who becomes an icon for his nuclear rule of thumb.

Walton Goggins Breaks Down Fallout’s The Ghoul & Finding The “Humanity” In His Gunslinger Character

Fallout’s Rule Of Thumb Test Is Based On A Real Nuclear Bomb Theory

Vault Boy’s signature thumbs-up is based on an old American protocol

The nuclear rule of thumb theory was so widely believed at one point that it was even taught as a standard procedure in American schools.

The Fallout mascot Vault Boy is the signature blonde-haired cartoon with a wide smile seemingly winking and holding up a thumb trying to encourage positivity and bright spirits. On the contrary, the thumbs-up emblem represents a much darker and more dubious intention, testing to see how close a nuclear mushroom cloud is. This notion is even reinforced by the lighting on the cartoon drawing of the blonde-haired man, with the areas of his face, suit, and thumb all brighter due to looking at a far-off nuclear explosion. This nuclear rule of thumb theory is a major part of both the Fallout video game and series and is explored more in the Amazon show.

Although Vault Boy is only a fictional mascot of Vault-Tec Corporation, the nuclear rule of thumb test seen in Fallout was actually an old belief based on an antiquated and misleading nuclear bomb theory. It was so widely believed at one point that it was even taught as a standard procedure in American schools. According to Inverse, “Americans used to be taught that if a nuclear bomb exploded in the distance they should hold out their arms, stick up their thumbs, and see if the cloud was bigger or smaller than their opposable digit. If the cloud was bigger than your thumb, teachers explained, you’d know that you were in the radiation zone and should start running.“

Would Fallout’s Rule Of Thumb Work With Real Nuclear Blasts?

The Fallout rule of thumb shouldn’t be used in a real-life event

The nuclear thumb theory that inspired Vault Boy and is used by Cooper in Fallout should not be considered an actual rule for nuclear explosions.

Despite being a true American protocol response to nuclear warfare at one point, the nuclear rule of thumb theory is no longer supported or encouraged and has since become antiquated in modern society. For this reason and more, the nuclear thumb theory that inspired Vault Boy and is used by Cooper in Fallout should not be considered an actual rule for nuclear explosions. In the event of an actual nuclear fallout, in which a mushroom cloud can be seen far off in the distance as depicted in the opening scene of the Amazon series, people are simply encouraged to “get inside, stay inside, and stay tuned“, per the United States Department of Homeland Security and FEMA.

How The Fallout Show Uses The Rule Of Thumb Test

Cooper teaches his daughter about the test moments before the nuclear fallout

Cooper was the inspiration behind Vault Boy and the thumbs-up move, which became the mascot for the Vault-Tec Corporation in the Fallout series.

The nuclear rule of thumb test is one of the first ways that viewers of Fallout are introduced to the premise and story world of the Amazon series. In the very first scene of Fallout episode 1, aptly titled “The End”, Cooper shows his young daughter how to use the thumb theory in a hypothetical nuclear situation. His daughter is having a birthday party with many kids and parents over their house, all piled together inside a living room made of glass. This makes the inevitable shockwave after the nuclear fallout even more devastating, as Cooper’s daughter uses the rule of thumb that her father had just taught her.

Later in the series, the audience learns that Cooper was the inspiration behind Vault Boy and the thumbs-up move, which became the mascot for the Vault-Tec Corporation. This nuclear rule of thumb theory wasn’t originally a part of the Fallout game lore. Instead, it started as a fan theory that was initially debunked by the video game’s developers. The creators of the Fallout Amazon series, however, decided to make the nuclear rule of thumb part of the canon narrative in the television adaptation, marking a big change from the original game but also arguably adding a great improvement to the Fallout lore.