On 18 Dec, 09:45, disgoftunwells wrote:
Humans have a problem with cards because you don't know how much money
you have left on the card.

That's why [a tiny subset of] people are interested in mobile phone
near-field communications. Basically the "card" is embedded in the
phone, and you can check the balance and load credit onto it using the
phone's screen and internet connection.

U