While the stamps on this envelope might look similar, keen-eyed viewers might have noticed they cost different amounts in entirely different currencies! It’s likely this was done deliberately, to mark the changeover from pre-decimal currency on Australian stamps.

Before 1966, Australians used a difficult and complicated currency system inherited from Britain: the pound (£) divided into 20 shillings (s), and a shilling into 12 pence (p), which meant that £1 equalled 240 pence. Tired of a system that required complex arithmetic for even simple transactions, the need for a more efficient currency was made clear for the growing nation.

Australia decided to switch to its decimal currency system on ‘Changeover Day’ or ‘C-Day’ on February 14th, 1966. Driven by practical reasons, it aimed to simplify transactions and improve national productivity. The transition also reflected Australia's increasing independence and modern identity, moving away from its colonial ties to Britain.

Prior to C-Day, a public competition was held to seek suggestions for naming the new Australian currency which produced submissions like Austral, Oz, Boomer, Roo, Kanga, Emu, Koala, Digger, Zac, Kwid and Dinkum! A staunch monarchist, the then Prime Minister Menzies rejected these, preferring the ‘Royal’ but this was in turn rejected in favour of the ‘dollar’.

A comprehensive public education campaign was launched to prepare Australians for the changeover. Central to this campaign was Dollar Bill, a cartoon character who appeared in various media forms, such as this animated short with a catchy jingle.

This jingle, along with other advertisements, educated the public on the new system. The campaign was highly successful, with songs and slogans becoming well-known and helping to ensure a smooth transition on "C-Day.”

It was an important feature of the new coins that they would be produced in Australia by Australian organisations. The Royal Australian Mint opened a year before C-Day and were able to stockpile about one billion coins in preparation.

The new designs by Stuart Devlin were described by Prime Minister Harold Holt as a ‘family’ of Australian motifs. In addition to the echidna, lyrebird, platypus and coat of arms still in circulation today, the feather-tail glider and frilled-neck lizard designs for the one-cent and two-cent coins which were later withdrawn from circulation in 1992; many of them were actually melted down to create the bronze medals for the 2000 Olympic Games in Sydney.

To prepare Australians for the new system, the Reserve Bank of Australia published an information pamphlet which featured the important new decimal rules:

One Dollar = 10 Shillings
100 Cents make One Dollar
So 50 Cents = 5 Shillings
20 Cents = 2 Shillings
10 Cents = 1 Shilling and
5 Cents = Sixpence*

* Written as 6d, half of one shilling.

Easy right? The pamphlet also included a few ‘simple puzzles’ to test readers’ decimal currency knowledge. Are your mathematic skills up the task?