Sources

Every source backing a fact on Philip Gray's own page, deduplicated — the same source backing several facts appears once.

• Second Workshop on Human Computer Interaction with Mobile Devices — https://www.dcs.gla.ac.uk/mobile99/
• https://link.springer.com/book/10.1007/3-540-45756-9 — https://link.springer.com/book/10.1007/3-540-45756-9
• https://link.springer.com/book/10.1007/b100594 — https://link.springer.com/book/10.1007/b100594