San Francisco (sans-serif typeface) and iOS 10 is a new variant named "SF Compact Rounded". It is used in the new contact placeholder icons introduced in the OSes. The "SF Serif" variant was showcased during the keynote at WWDC 2018 on June 4, 2018 when the all-new Apple Books app was introduced. This variant is exclusive to Apple Books in iOS 12 and macOS Mojave, is not mentioned in Apple's Typography design guidelines, and is not publicly downloadable like other variants of the San Francisco typeface. Since its introduction, San Francisco has gradually replaced most of Apple's other typefaces on their software and hardware
Helvetica used Helvetica as the system typeface of iOS until 2015. Helvetica has been widely used by the U.S. government; for example, federal income tax forms are set in Helvetica, and NASA used the type on the Space Shuttle orbiter. Helvetica is also used in the United States television rating system. The Canadian government also uses Helvetica as its identifying typeface, with three variants being used in its corporate identity program, and encourages its use in all federal agencies and websites. In the European Union, Helvetica is legally required to be used for health warnings on tobacco products such as e.g.