HK’s power over its currency similar to that of states [China Daily]
Some of the expressions of Hong Kong’s autonomy are large and politically contentious — immigration and economic regulation come to mind. However, other expressions of autonomy can be seen in our day-to-day lives. One clear symbol can be found in any wallet, in the purple, green, red and brown bank notes of the Hong Kong dollar. Hong Kong is, perhaps, the only city, apart from Macao, governed under the same rules, that prints and administers its own currency.
This leads into a greater power — the ability to control the value of a currency. A country with its own currency can alter how much it is worth, both domestically and internationally. Many states let their currencies float freely on the international market; others, such as China, choose to manage the value of their currencies to suit economic conditions, at least to some degree.