Certified gold necklace"...Certified by whom
I will give the young lady who got it a Certificate of Competance.
Interesting this decimalisation lark. Australia and South Africe went for 10 shillings as the datum for the new Dollar or Rand. It was easy, really, as all the existing coins but the penny were a decimal ranging from 5% to 25%. It also got them out of the Sterling Area so they were in control of their own currency. New Zealand and Rhodesia followed and in my experience a year or so before the changeover coins had both currencies stamped on the back, ie 2/- 20c. Pennys increased in value by 20% until new ones were minted but with the number in circulation it wasn't worth bothering about.
The Brits went for the Pound, the biggest unit of currency in the world and then they had to change ALL the coinage overnight. The cynic would argue that the reason they kept the original pound was because of the hordes tucked away in the Indian sub-continent and it was better for them to continue to be tucked away and therebye save the Bank of England the embarrassment of having to redeem them.
IIRC there was also a major spike in inflation when it happened.