Twitter generates revenue principally from the sale of advertising services and, to a lesser extent, from entering into data licensing and other arrangements. In the notes to the statements, it explains that: "The Company's advertising services include three primary products: (i) Promoted Tweets, (ii) Promoted Accounts and (iii) Promoted Trends. Promoted Tweets and Promoted Accounts are pay-for-performance advertising products priced through an auction. Promoted Trends are featured by geography and offered on a fixed-fee-per-day basis. Advertisers are obligated to pay when a user engages with a Promoted Tweet or follows a Promoted Account or when a Promoted Trend is displayed. Users engage with Promoted Tweets by clicking on a link in a Promoted Tweet, expanding, retweeting, favoriting or replying to a Promoted Tweet or following the account that tweets a Promoted Tweet." When do you think that Twitter should be recording revenue?