Revolver (Beatles album) group collective since 1962, and gave them an unprecedented amount of time to prepare for a new album. Writing in "The Beatles Forever", Nicholas Schaffner cites 1966 as the start of the band's "'psychedelic' period" and adds: "That adjective implies not only the influence of certain mind-altering chemicals, but also the freewheeling spectrum of wide-ranging colors that their new music seemed to evoke." Music journalist Carol Clerk describes "Revolver" as having been "decisively informed by acid", following John Lennon and George Harrison's continued experimentation with the drug LSD since the spring of 1965.<ref name="Clerk/Uncut"> Available at Rock's Backpages (subscription required).</ref>
1 (Beatles album) of America. The album is the best-selling album of the 21st century in the US and the fourth best-selling album in the Soundscan era (1991–present). As of February 2014, the album has had sold 12,410,000 copies in the US. In the US, the album secured the Beatles a fourth decade in which they placed an album at number 1 on the "Billboard" chart. In Canada, "1" debuted at number 1 on the Canadian Albums Chart, selling 54,668 copies in its first week. The album was certified Diamond (1,000,000 units) by the CRIA in February 2001, just four months after its