- " 'Hey, kid,' the old guy called as Marty walked past, 'can you thumb a hundred bucks to help save the clock tower?' He held out a silver box with the inscription 'Portable Thumb Unit'. / Marty hesitated. / 'It's an important piece of history,' the other guy added earnestly. The circular name patch over his pocket said his name was 'Terry'. "
- —From Back to the Future Part II by Craig Shaw Gardner (quote, page 49)
Portable thumb units are rectangular shaped handheld electronic wireless devices with fingerprint scanning technology used in 2015 to collect donations and other funds where a person was unable to access a teller.
- In 2015 as well as prior years, rectangular-shaped handheld electronic tablets with fingerprint scanners are commonplace, and are used to make payments using fingerprints.
- Back to the Future Part II
- Back to the Future Part II novelization (First identified as Portable Thumb Unit)