The interdimensional extrapolator is a device that Cisco Ramon created that allows the user to open an interdimensional breach between points of space, both in the same universe and between others.
Team Flash has an interdimensional extrapolator on hand, should they need it.
Wishing to give Kara Danvers the ability to travel between Earths herself, Cisco Ramon created the interdimensional extrapolator and gave it to her as a gift, explaining that it had communication functionality between their dimensions. Kara later used it, opening a small breach from Earth-1 to Earth-38, traveling between them.
Sometime later, Winn Schott examined the device, being impressed by it. When the D.E.O. brought in a new prisoner, he hypnotized Kara, broke out of his handcuffs and took the interdimensional extrapolator, using it to transport himself to Earth-1.
J'onn J'onzz and Mon-El presumably made use of Kara's interdimensional extrapolator when they brought her to Earth-1 to get help from Team Flash as well as pursue Music Meister after he "whammied" Kara.
Kara and Alex used it to transport themselves to Earth-1 for Barry Allen and Iris West's wedding. After their trip, during which they helped to prevent a Nazi invasion from an alternate universe, they used it to return to Earth-38.
Team Flash later enlisted Leo Snart's help to safely transport Neil Borman/Fallout into A.R.G.U.S. protective custody on Earth-1. Afterwards, Cisco gave Leo an interdimensional extrapolator of his own, suggesting that Leo and Ray, who were getting married, could use it to travel to Earth-1 for a honeymoon. Leo then used it to return to Earth-X.
When Team Flash was trying to come up with ideas of how to stop Cicada, Nora suggested that they enlist the help of another version of Harrison Wells. When Team Flash contacted Harrison Wolfgang Wells, he politely stated that he was too busy to help them, but instead recommended they turn to Harrison Sherloque Wells, regarding him to be the best detective in the multiverse, and gave Team Flash his coordinates. Since Cisco's hands had gotten cut in a fight against Cicada, thus making it painful to try to open a breach, Cisco used an interdimensional extrapolator to breach this new Wells to Earth-1.
After Nora was "whammied" by Spencer Young's phone, (she read a news article which hypnotized her into trying to kill Barry), Iris used an interdimensional extrapolator to breach herself to their location and knock Nora out with a tranquilizing dart.
Later, Barry was abducted by Rag Doll, who put power-dampening cuffs on the former and brought him to the top of a tall building, threatening to drop him. Since Cisco was still unable to open a breach due to his injuries, Iris contemplated using an interdimensional extrapolator to get herself to Barry's location to save him. However, this proved impossible since Sherloque had accidentally sat on the team's only interdimensional extrapolator, and Cisco stated that it would take him at least an hour to fix the device.
Caitlin, Barry and Cisco used an interdimensional extrapolator to breach themselves to the North Pole when they were searching for Caitlin's father, Thomas Snow. After they found him in an abandoned Tannhauser Industries black-ops site, the four of them then used the instrument to return to S.T.A.R. Labs. A short time later, Cisco used the extrapolator to return to the black-ops site where they'd found Thomas in order to investigate, as he suspected that Thomas was hiding something.
When Oliver and Barry each woke up one morning, and found that they'd swapped lives and realized that no one on Earth could tell who they really were, they decided to go to Earth-38 to find out if Kara would recognize Barry as Barry, and Oliver as Oliver, using Team Flash's interdimesional extrapolator to travel to her universe.
When rounding up meta-humans to transport them into protective custody in an effort to keep them safe from Cicada, Barry (as The Flash) approached Shawna Baez, a meta-human also known as Peek-a-boo (whom Team Flash had fought before), at a bar, asking her to come with him for her own safety. When Cicada showed up, Barry left Shawna with an interdimensional extraplator, telling her to use it get out of there. Barry then engaged in a fight with Cicada, seeking vengeance after Orlin had severely injured Nora; Barry's daughter from the future. However, he ended up having to retreat and go with Peek-a-boo, as she was having trouble figuring out how to work the device.
DC's Legends of Tomorrow