Cards with a magnetisable material printed in or on them (as found on the world's most popular credit, debit and prepayment cards). Gamma ferric oxide ink is the tradition soft magnetic material used. ISO standard magnetic stripe cards have three tracks of data, the first being assigned to the airline industry - accepts alphanumeric entries, the second to financial transactions - numeric content only, and the third being a rewriteable track designed for off-line magnetic stripe based transactions; it is rewritten each time. Magnetic stripe cards carrying non-standard stripes and multiple stripes are also used in large numbers for access control and storing value. Magnetic stripes are also applied to cardboard tickets.