Though overshadowed by the Great Depression, there is no shortage of ingenuity in the 1930s. The two-way radio gets miniaturized, and the world's first portable walkie-talkie goe on the air. The electric guitar changes popular music forever, and commuters become a cash cow for cities when the parking meter is introduced. Copying by hand and mimeographs go the way of the Dodo with the invention of Xerography. The airplane gets a nimble little brother in the air as the helicopter makes its debut.