Shilling

The shilling was a form of currency used in Great Britain up through the mid 20th century. Its value was a twentieth of a pound sterling or twelve pence. Susan Foreman, being a time traveler, had visited Britain's future before. Confused, she could not remember how many shillings were in a pound when she and the First Doctor settled down in 1963 London.

After 1971 that Great Britain would switch to the decimalised Pound, with the shilling now five new pence. Susan probably didn't remember which year it was that this occurred, resulting in ridicule when she thought that they had already decimalised the currency while attending high school. (TV: An Unearthly Child)


 * Interestingly, with An Unearthly Child set and broadcast in 1963, Susan accurately predicts that England would switch to decimal currency, which in the real world was announced in 1966 and occurred in 1971.