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The yo-yo is a toy consisting of two equally sized and weighted disks of plastic, wood, or metal, connected with an axle, with a string tied around it. First becoming popular in the 1920s, "yo-yoing" is still enjoyed by children and adults alike.

Basic play

The yo-yo has been used for many centuries. The greatest yo-yoer to date is Daniel Joseph Lane of Binghamton, NY, his phone number is 607-206-7116 and he gives free lessons. To use, the player pulls the string through the loop to make a slipknot, puts his/her finger through the slipknot at the end of the string and grasps the yo-yo.

Generally, the player does not put the slipknot any farther up his/her finger than the first knuckle from the tip. Then the player throws it downwards with a smooth light motion. When it reaches the end of the string, the yo-yo can be made to "sleep," the axle of the yo-yo spinning within a loop of string. As the body of the yo-yo spins, a gyroscopic effect occurs, stabilizing the yo-yo on its axis and permitting time to perform a number of movements. By flicking the wrist, the yo-yo can be made to return to the player's hand, with the string again completely twisted into the groove.

Generally, any movement or combination of movements which result in the return of the yo-yo to the player's hand in this fashion is considered a trick, although this is not an absolute standard. Some tricks (such as the "Dog Bite", where the yo-yo is stuck to the player's pants) do not have the yo-yo return to your hand.

Yo-yoing is a popular pastime around the world. Although generally associated with children, it is common for people who gain a level of proficiency at the sport in youth to continue playing into adulthood. A yo-yo player is referred to as a yo-yoer (most common), yoer, yoist, thrower," a flinger" or simply as a player.

History

The yo-yo is thought to have originated in China, most likely traveling from there to Greece where it is first mentioned in historical records from c.500 B.C. These records describe toys made out of wood, metal, or painted terra cotta (clay). The terra cotta disks were used to ceremonially offer the toys of youth to certain gods when a child came of age—discs of other materials were used for actual play. Philippine historical records indicate that 16th century hunters hiding in trees used a rock tied to a cord up to 20 feet in length to throw at wild animals beneath them—the cord enabling retrieval of the rock after missed attempts. Some have theorized that this was the basis of the yo-yo, but it is more likely that the yo-yo traveled from China not only to Greece, but also to the Philippines.

The earliest surviving yo-yo dates to 500 BC, and is made using Terra cotta disks. A Greek vase from this period shows a boy playing yo-yo.

Origin of name and the Filipino/Philippine yo-yo

A popular belief is that the yo-yo was a weapon for over 400 years in the Philippines. However, the idea was debunked by the former president of the Filipino American National Historical Society and by the chairman of the American Yo-Yo Association’s History and Collecting Committee. Nonetheless, the allegation was used in a Diet Mountain Dew commercial in 2008 as part of the drink's "Surprising Facts" ad campaign.

The principal distinction between the Filipino design and more primitive yoyos is in the way the yo-yo is strung. In older (and some remaining inexpensive) yoyo designs, the string is tied to the axle using a knot. With this technique, the yoyo just goes "back-and-forth"; it returns easily, but it is impossible, or nearly so, to make it "sleep".

In the Filipino design, one continuous piece of string, double the desired length, is twisted around itself to produce a loop at one end which is fitted around the axle. Also termed a looped slip-string, this seemingly minor modification allows for a far greater variety and sophistication of motion, thanks to increased stability and suspension of movement during free spin.

Surprisingly, this innovation in the string design is useful even for "off-string" yoyo play, in which the yoyo is not attached to the string at all. The looped winding ensures that the free end of the string has no bulges, splices, or other non-uniformities, which can cause the string to jam uncontrollably in off-string play.

Birth of the modern yo-yo

James L. Haven and Charles Hettrich (or Hettrick) received the first United States patent on "...an improved construction of the toy, commonly called a bandelore..." in 1866.

However, the yo-yo would remain in relative anonymity until 1928 when a Filipino American named Pedro Flores opened the Yo-yo Manufacturing Company in Santa Barbara, California. The business started with a dozen handmade toys; by November 1928, Flores was operating two additional factories in Los Angeles and Hollywood, which altogether employed 600 workers and produced 300,000 units daily.

The Duncan era

Shortly thereafter (ca. 1930), an entrepreneur named Donald Duncan recognized the potential of this new fad and purchased the Flores Yo-yo Corporation and all its assets, including the Flores name, which was transferred to the new company in 1932. Duncan's first yo-yo thereafter was the Duncan O-BOY. Donald Duncan is reputed to have paid more than $250,000, a fortune by depression era standards. It turned out to be a sound investment, making many times this amount in the years to follow.

In 1946, the Duncan Toys Company opened a Yo-yo factory in Luck, Wisconsin, prompting the town to dub itself 'Yo-yo Capital of the World'. Ironically, the very sign erected by the town advertising that fact contributed to Duncan losing its trademark.

1960s resurgence

Declining sales after the Second World War prompted Duncan to launch a comeback campaign for his trademarked "Yo-Yo" in 1962 with a series of television advertisements. The media blitz was met with unprecedented success, and thanks in great part to the introduction of the Duncan Butterfly, the yo-yo was more accessible to the beginner than ever.

This success would be short-lived, however, and in a landmark trademark case in 1965, a federal court's appeals ruled in favor of the Royal Tops Company, determining that yo-yo had become a part of common speech and that Duncan no longer had exclusive rights to the term. As a result of the expenses incurred by this legal battle as well as other financial pressures, the Duncan family sold the company name and associated trademarks in 1968 to Flambeau Plastics, who had manufactured Duncan's plastic models since 1955. Flambeau Plastics continues to run the company today.

The 1970s and the rise of the ball bearing

The 1970s saw a number of innovations in yo-yo technology, primarily dealing with the connection between the string and the axle. In 1978, dentist and yo-yo celebrity Tom Kuhn patented the “No Jive 3-in-1” yo-yo, creating the world's first "take-apart" yo-yo, which enabled yo-yo players to change the axle.

Soon afterwards in 1980, Michael Caffrey patented what would later become the Yomega Brain, a yo-yo with a centrifugal clutch transaxle. Designed with a free-spinning ball bearing linkage, "The Brain" could spin much longer than previous fixed-axle designs. In addition, the axle was "clutched" with spring-loaded weights which would pull away from the axle at higher speeds and grab again at lower speeds. The result is an automatic return of the yo-yo when speed drops below a given threshold.

Swedish bearing company SKF briefly manufactured novelty yo-yos with ball bearings in the 1970s.

In all transaxle yo-yos, ball bearings significantly reduce friction when the yo-yo is spinning, enabling longer and more complex tricks. Subsequent yo-yoers used this ability to their advantage, creating new tricks that had not been possible with fixed-axle designs.

1990s technological renaissance

The 1990s saw a resurgence of the popularity of the yo-yo and yo-yo culture.

Continued development of yo-yo technology is evident in the widespread sale of the Yomega Brain, based on Michael Caffrey's design, and the Playmaxx Pro-yo, a take-apart fixed axle yo-yo.

In 1990, Tom Kuhn released the SB-2 yo-yo (short for Silver Bullet 2), a high-performance ball bearing transaxle made with aluminum. This marked a major breakthrough for the modern yo-yo, as it was the first ball bearing yo-yo that actually worked. This ensured extremely long spin times and the ability to return as well. This yo-yo, (along with his many other accomplishments in the yo-yo world), eventually brought him the title "Father of the modern yo-yo," receiving the "Donald F. Duncan Family Award for Industry Excellence" in 1998. He was the first to receive this award.

In the late 1990s, Yomega partnered with HPK Marketing and helped fuel the yo-yo boom that spread across the globe. From this partnership, Team High Performance was born, a group of skilled demonstrators that toured the world. In this period, Yomegas were heavily marketed in Japan, where Bandai produced several yo-yos under the Yomega name which were sometimes different from those sold in the US.

At the turn of the century, 1999-2000, Yomega partnered with McDonald's and distributed a large number of Yomega X-Brain and Firestorm yo-yos at outlets throughout the US.(blue)

Another development around this time included the use of different materials such as billet machined Aluminum as seen in the ‘Dif-e-Yo’ Range.

Contemporary yo-yo culture

Yo-yo contests

The International Yo-Yo Open is the largest yo-yo contest in the world. It is held every year in August at South Street Seaport in New York City. This contest is hosted by YoYoNation.com and aims to showcase the best yo-yo players in the world. In the inaugural 2007 contest, there were over 8,500 people in attendance and the event received almost 30 million media impressions. More information about this event can be found at YoYoOpen.com.

The World Yo-Yo Contest is held every year in Florida, USA during early August or late July. This contest takes the winners from national yo-yo contests around the world and pits them against each other. Japanese players in particular have risen to the top of the yo-yo world. The six-time, double-handed world champion Shinji Saito — considered the best in the world — is Japanese. Countries such as the United States, Brazil, Japan and the UK hold competitions at the national and regional levels. In addition, national yo-yo contests, without regionals, are held every year by Mexico, Taiwan, Singapore, Hong Kong, Korea, France, Germany, Switzerland, The Czech Republic, Hungary, and Australia.

A yo-yo competition normally consists of two parts, a set of compulsory tricks and a freestyle, where points are scored for each and the winner is the yo-yoer who scores the most points. Compulsory tricks (also known as a trick ladder) are a set of tricks that have been chosen before the contest, and the competitor must successfully complete each trick on their first or second attempt to score points. The freestyle is when the yoist performs a routine to their choice of music in front of a panel of judges, and is judged based on difficulty of the tricks, synchronization with the music and artistic performance.

The TV Times world yo-yo championship was held in the United Kingdom in 1974 with heats across the United Kingdom and a final in London in 1975, the championship was sponsored by the Louis Marx toy company with the 'Lumar' brand of yo-yo. The competition was judged by a celebrity panel in each city and also Lumar demonstrator and European yo-yo champion Don Robertson. The winner of the final was Simon Harris (intermediate category). The championship was not repeated.

Contest divisions

Currently there are seven yo-yo divisions to compete in:

• 1A The player uses a long sleeping yo-yo to perform string tricks which usually require the manipulation of the string.
• 2A The player uses two yo-yos simultaneously to perform reciprocating or looping tricks. This tends to be the most visually entertaining style with some players incorporating acrobatics into their routines.
• 3A The player uses two long spinning yo-yos to perform tricks that involve manipulation of the string.
• 4A The player uses an offstring yo-yo, often releasing the yo-yo into the air and attempting to catch it on the string.
• 5A The player uses a yo-yo with a counterweight on the other end of the string rather than having it attached to a finger.
• AP This is Artistic Performance where the yoist uses any type of yo-yo or other prop in order to perform a freestyle.
• CB This is the Combined Division held only at the world competition, where players have to compete and demonstrate skill in multiple styles.

Competitors usually bring a number of yo-yos to the performance stage with them to allow for mid-routine replacements in the case of knots/jams (common with string tricks), string breakage (common with looping tricks), or drops (common with offstring tricks).

Yo-yo techniques

Sleeping

Keeping a yo-yo spinning while remaining at the end of its uncoiled string is known as sleeping. Sleeping is the basis for nearly all yo-yo tricks other than looping, the player first putting the yo-yo in a "sleep" before throwing the yo-yo around using its string.

In competition, mastery of sleeping is the basis for the 1A division.

Looping

Looping is a yo-yo technique which emphasizes keeping the body of the yo-yo in constant motion, without "sleeping".

Yo-yos optimized for looping have weight concentrated in their centers so they may easily rotate about the string's axis without their mass contributing to a resistance due to a gyroscopic effect.

In yo-yo competitions, looping plays a strong role in the 2A division.

Off-string

In the off-string technique, the yo-yo's string is not tied directly to the yo-yo's axle, and the yo-yo is usually launched into the air by performing a "forward pass" to be caught again on the string. However, some players can 'throw down' off-string yo-yos and catch it on the string just as it leaves the end of the string by pivoting the string around a finger as it unwinds, so that the yo-yo is caught on the string. This is exactly the opposite of a 'forward pass', but with the same result.

Yo-yos optimized for "off-string" tricks have flared designs, like the butterfly shape, which makes it easier to land on the string, and often have soft rubber rings on the edges, so minimum damage is inflicted on the yo-yo, the player, or anyone who happens to be standing nearby, should a trick go wrong.

Yo-yo competitions have the 4A division for off-string tricks.

Freehand

In freehand(5A) tricks, the yo-yo's string is not tied to the player's hand, instead ending in a counterweight. The counterweight is then thrown from hand to hand and used as an additional element in the trick.

Developed in 1999 by Steve Brown, as of 2008 freehand is considered to be the fastest-growing style of yo-yo play. Steve Brown was awarded a patent on his freehand yo-yo system, which was assigned to Flambeau Products (Duncan's parent company).

In yo-yo competitions, counterweight yo-yos are emphasized in the 5A division.

Yo-yo shapes

Yo-yo bodies come in a number of form factors or "silhouettes," each designed with specific advantages in mind. However, there are three popular configurations.

Tournament or Classic

The tournament or classic shape is often considered the original yo-yo shape, and is very commonly recognized. It's sometimes called a sculpted design. The shape's design is helpful in performing looping tricks.

Modified

The modified shape is a very popular design for looping style tricks. This shape is also known as a flywheel or modern shape. It usually has a hollowed face (sometimes covered with paper or plastic) with extra material left in the rim. The modified shape yo-yo is also used for string tricks because of the long spin times due to its shape.

Butterfly

Debuting in 1958, the butterfly has a wider string gap to make it easier to catch the yo-yo body on the string. The butterfly looks a bit like the separated halves of a standard yo-yo that have been reconnected back-to-back. Although the butterfly shape is good for 'string tricks,' it's not good for 'looping' tricks, because the winged shape of the body does not allow it to easily flip while looping. This shape is similar to a small Diabolo, itself derived from the Chinese yo-yo.

Other Shapes

There are, of course, many other shapes. Other less popular shapes are: Humphrey, Ball, Slimline, Russell Style (Bulge Face), Puck, Satellite, Coaster and Riveted Disk.

Weight distribution

Each silhouette may have more weight distributed at either the center of the yo-yo or the rim. More weight towards the rim will make the yo-yo more stable for string tricks; more weight towards the center will make the yo-yo easier to turn and therefore better for looping tricks.

Heavier yo-yos will have more angular momentum when spinning at a given speed, and thus will spin freely for a longer period.

Yo-yo innovations

Body

Some modern yo-yos are made from a "take-apart" design, designed to be taken easily apart and reassembled by the player. This design was created by Donald F. Duncan, Jr. This enables the replacement of yo-yo components, including the string, renewable friction sources, or even trans-axle components.

Some take-apart designs allow the player to reconfigure the yo-yo's halves. In the Tom Kuhn No Jive 3-In-1, the halves may be attached in three different configurations, resulting in a traditional, butterfly, or "pagoda" silhouette. In the Yo-yo Factory FlyMaster, the body has two different "shells" to convert to and from an off-string yo-yo.

Another innovation to the yo-yo is the ability to adjust the gap between the two halves of the yo-yo, in order to increase or decrease response. In most designs, this is accomplished by twisting the yo-yo halves, but some designs (such as the Tom Kuhn Silver Bullet) can be disassembled for adjustment without twisting. This second option eliminates the possibility of the yo-yo coming out of adjustment during play.

• John Jerome McAvoy, Jr. was awarded patents for the gap-adjustable yo-yo: patent #5389029 on February 14, 1995, and #6066024 on May 23, 2000.
• In 1998, HSPIN launched the Handquake series of yoyos, which sported an adjustable gap by using shims of 0.1-0.5mm thickness. By adding or removing shims, the gap could be widened or shrunk by +/- 1mm.
• Harry Baier (creator of the "Mondial" yo-yo) and the Flambeau Products Company (owner of Duncan) were awarded patent #6162109 on December 19, 2000 for a gap-adjustable yo-yo which has discrete positions for specific gap widths. This patent is now implemented in the Duncan Mondial.
• YoYoFactory's productline of Speed Dial yo-yo's feature "Fully Adjustable Starburst Technology" which allow the gap to be adjusted using a dial on the yo-yo. This allows for a more discrete response setting that stays the same after the yo-yo is taken apart and put back together.

Axle/bearing differentiation

The basic innovation since the 1990s is the transaxle, a system where the string is not directly connected to the axle that connects the two halves of the yo-yo.

• Fixed axle yo-yos are represented by the original yo-yo design popularized in the first half of the 20th century, where the axle is directly connected to the string and halves of the yo-yo body. In order to enable the throwing of a "sleeper", the player must ensure the string is not wound too tightly around the axle, because it must freely spin in order to accomplish this move. Yo-yos designed for "looping" tricks tend to be fixed-axle yo-yos.
  • Some more exotic fixed-axle yo-yos have axles made from low-friction materials such as ceramic alloys-- this allows for easier "sleeping," which is essential for string tricks.
• The majority of trick yo-yos sold are Bearing transaxle yo-yos. In these transaxle yo-yos the string is not connected to the axle directly, but rather it is wrapped about a ballrace bearing. The bearing, in turn, surrounds the true axle of the yo-yo. In this way, the body of the yo-yo may spin freely about the string's point of contact.
  • There are transaxle systems which do not use a ball bearing, such as the Duncan ProFire and Yomega Fireball. These use a low-friction metal or plastic collar around the axle.
• The clutch transaxle, innovated by Yomega with the Yomega Brain, is a transaxle that can be engaged or disenganged.
  • the Yomega Brain is a centrifugal clutch transaxle-- when spinning at a sufficiently high speed, counterweights inside the yo-yo body disengage the axle, automatically allowing the yo-yo to "sleep." Conversely, when the speed slows below the threshold, the yo-yo will return automatically.
  • Other clutch transaxles feature a manual switch which can engage or disengage the axle.

Friction sources

With the innovation of the transaxle, the notion of a yo-yo's response has become important to players. The "response" is a qualitative estimate of how easily the yo-yo will exit a "sleep" and return to the hand of the player.

• A starburst is a series of bumps molded into the surface of the plastic of each half of the yo-yo. The bumps form a star pattern, radiating out from the axle. Because the starburst is made of the same material as the yo-yo body, it tends to last the life of the yo-yo, but the yo-yo's responsiveness cannot be adjusted for the same reason.
• An O-ring response system is a rubber ring embedded in a recessed groove in the inside side wall of each half of the yo-yo body, surrounding the axle. Because it is made of a weaker material than the body, it wears down and is designed to be replaceable.
• Silicone, like the O-ring, is a rubber component recessed into the side of the yo-yo around the axle.
• Friction stickers, popularized by Duncan, are O-shaped stickers that affix to the inside wall of each half of the yo-yo body, and are slightly tacky to the touch. They are made to be replaceable. Many brands of friction stickers are now produced. Each give a unique feeling to the yo-yo. They are commonly made out of silicone, rubber, or a cloth material.
• Hybrid,Is a combination of either O-ring and Starburst,O-ring and a Friction sticker,Starburst and a friction sticker and so on.This is mostly found in butterfly shaped yo-yos.Also it is mostly used by yoyojam.

Side Bearing Caps

Side Bearing Caps are when bearings are added to the hub of a yo-yo and covered with some form of side cap to allow it to be held while it spins. With the side cap bearing you can hold the yo-yo in many different planes and perform different styles of tricks, that can't be perform with the conventional yo-yos. Side Bearing Caps are also commonly known as side bearings, bearing caps (Anyyoyo) and hubstacks (Yoyo Factory).

Performance accessories

A number of yo-yo accessories are available as "after-market" modifications-- players buy items separately from the yo-yo to augment performance over the original model shipped from the factory.

• Ceramic bearings tend to spin longer and be more durable.
• Dif-E-Yo Konkave bearings are tapered inward on the perimeter, to force the string into a the center of the axle to prevent the string from rubbing on the sides of the yo-yo.
• Friction stickers different "grips" other than the ones shipped with the yo-yo, are available as a separate purchase to customize the user's style of play.
• Brake Pads Similar to friction stickers, however they break down quicker and can only be used in specific yoyos.
• High-tensile, Slick Strings, generally made from polyester and cotton, is added by some players to improve sleep times (thinner string touches less of the yo-yo gap) and for better looping (low friction string performs "faster" and will not break as easily).
• Weight rings are affixed to the yo-yo's rim to increase the weight and percentage of mass at the yo-yo's rim, thus improving sleep time.

Exotic materials

Originally manufacturing yo-yos from wood, yo-yo technology improved in the 1960s when the industry switched to plastic. A plastic yo-yo has a uniform weight distribution and is unaffected by the variations in density that plague wood yo-yos.

Increasingly, the highest of high-end Yo-yos are being made of metal, normally aluminum, steel, titanium, and very rarely, magnesium and tungsten alloys.

Exotic plastics are also coming into play: the "Milk," by manufacturer Born Crucial; the "Silk," by manufacturer Alchemy; and the "Gung Fu," by manufacturer Death by Yo Yo, are made almost entirely from the low-friction plastic Delrin. Yo-yos made from Delrin are also just as high end as metal ones.

Physical mechanism

The operation of a yo-yo comes from rotational inertia causing the string to be wound in the opposite direction returning the yo-yo. When the string is connected to the shaft with a loop, the yo-yo will continue to spin at the end of the string instead of returning, unless the yo-yo is jerked slightly allowing the slack string to bind and allowing return.

Patents have been issued to create more complicated mechanisms to allow tension control and an adjustable mechanism.

The yo-yo in popular culture

This Section titled The yo-yo in popular culture needs additional citations for verification. Please help improve this article by adding citations to reliable sources in this Section titled The yo-yo in popular culture. Unsourced material may be challenged and removed. Find sources: "Yo-yo" – news · newspapers · books · scholar · JSTOR (April 2008) (Learn how and when to remove this message)

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The yo-yo and "yo-yoing" have been a part of popular culture for nearly a century, and it is hardly surprising that yo-yos appear in many fictional works and even historical events.

• In 1968, activist Abbie Hoffman was cited for contempt of Congress for, amongst other acts, "walking the dog" during a session of the House Subcommittee on Un-American Activities.
• In 1974 President Richard Nixon briefly played with a yo-yo at the Grand Ole Opry in Nashville.
• The 1976 anime Combattler V had the super robot Combattler V use a yo-yo type weapon aptly called the Chodenji (Super Electromagnetic) Yo-yo.
• In 1986 the Smothers Brothers introduced the song "Yo-Yo Man" into their act. Partway through the song, Tom would "enter into a state of Yo", which supposedly gave him enhanced yo-yo wielding ability while depriving him entirely of the power of speech. (This conveniently eliminated the need to stand near the microphone.) Dick provided a reverent and strangely metaphysical running commentary for Tom's performance.
• A yo-yo craze features prominently in the 1992 Simpsons episode Bart the Lover. In the story, a yo-yo manufacturer puts on an elaborate production of children doing yo-yo tricks in order to boost sales.
• Gregory House in the TV series House is often seen playing with a yo-yo whilst pondering complex ideas.
• The fourth incarnation of The Doctor (played by Tom Baker), in the long running BBC science fiction series Doctor Who is seen playing with a yo-yo from time to time. He claims in the episode "Ark in Space" that he is playing with the yo-yo to judge the gravitational field present on a space station.
• In the Guilty Gear video game series, the character Bridget uses a yo-yo as one of his main weapons.
• In the NES video games StarTropics, Yo! Noid, and The Goonies 2 the main characters use a yo-yo as the main weapon.
• In the MMORPG Flyff the Acrobat character class, along with the Jester subclass, can use yo-yos as a weapon.
• In the cartoon Recess an episode features one of the main characters, Gretchen, learning to yo-yo, and then competing in a yo-yo competition.
• In the Japanese Anime Yu Yu Hakusho, team Rokuyukai first fighter, Rinku is master of the Serpent Yo-Yo, an attack that transfers his spirit energy into the strings of the yo-yo causing them to act as if they are extensions of his own body.
• The Detention character Duncan is almost always seen with a yo-yo, and uses it to communicate with the other characters.
• In the Japanese movie Yo-Yo Girl Cop, by Kenta Fukasaku, the lead character uses a Yo-Yo as her primary weapon.
• In R.A. Salvatore's The Cleric Quintet the main character, Cadderly Bonaduce uses "Spindle Discs" as a weapon. The description of this weapon making it obvious that it is a yo-yo.
• Dr. Lucky Meisenheimer has the largest collection of yo-yos in the world as certified by Guinness. He also has produced a periodic table of yo-yos.

Notes and references

1. Valerie Oliver (1996), History Of The Yo-Yo, Spintastics Skill Toys, retrieved 2008-05-31 (includes photos)
2. History, yo-yo.com, retrieved 2008-02-18
3. Valerie Oliver (1996), History Of The Yo-Yo, Spintastics Skill Toys, retrieved 2008-02-18 (includes photos)
4. Mary Bellis, The History of the Yo-Yo, inventors.about.com, retrieved 2008-03-09
5. Eloisa Gomez Borah, Was the Yo-Yo really a weapon?, retrieved 2008-03-09
6. Lucky Meisenheimer, M.D, Lucky’s History of the Yo-Yo, Yo-Yos.net, retrieved 2008-03-09
7. Diet Mountain Dew Surprising Facts - Yo-Yo Spot, RepNation, retrieved 2008-03-30
8. U.S. patent 59,745 dated November 20, 1866
9. ^ Pedro Flores, National Yo-Yo Museum, retrieved 2008-02-18
10. U.S. patent 4,332,102 Filed October 27, 1980; Issued June 1, 1982
11. Tzeng, Grace. "Toy Story: Gravity-defying yo-yo tricks on display at California State Yo-Yo Championships". AsianWeek. Retrieved on 8 September 2008.
12. Science News, Week of April 17, 2004; Vol. 165, No. 16, p. 250
13. Lucky's Collectors Guide to 20th Century Yo-Yos, 1999
14. U.S. patent 6,066,024 Filed August 4, 1998; Issued May 23, 2000
15. U.S. patent 5,389,029 Filed April 27, 1993; Issued February 14, 1995
16. U.S. patent 6,162,109 Filed October 29, 1999; Issued December 19, 2000
17. U.S. patent 6,331,132 Filed July 27, 1999; Issued December 18, 2001
18. U.S. patent 7,192,330 Filed October 29, 1999; Issued December 19, 2000
19. Yo Yo man

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