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 traveller, 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. She thought that they had already decimalised the currency. (TV: An Unearthly Child)

Behind the scenes
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.