Currency

Just as in a real economy in an RPG the type and value of the currency used in the game universe is an important consideration for the Player Characters. Barring the progressive social background of Star Trek, where they don't use money, in almost every other Sci-Fi universe the venerable Credit is often the currency of choice.
Part of the framework of Natural Law is the concept that value is inherent to certain things. The value of a human is based on the divine spark which is contained in him or her. The value of work is in the wealth that is created in its effort. Money is substitute for the labor that is inherent in the wealth it creates or in the material goods which can be traded for that money.
Now throughout history there have been two ways to use money to keep track of wealth. One way is through the use of money made of a substance which is of itself considered to have value, typically a precious metal, although at certain time and places gemstones or even rocks have been used. The other method is through fiat money.
The Song dynasty of China was the first known government to use fiat money. Inflation became so rampant that by the 15th century the Ming Dynasty ended it's use. Eventually every country which has ever used fiat money has experienced hyperinflation and economic collapse.
Governments who wish for long term economic stability do not use fiat money.
The Highland government instead uses commodity money, that is money whose value comes from the commodity out of which it is made. Because it has intrinsic value Highland money is accepted almost everywhere even in the Wilds.
To compare the value of individual denominations of Highland money to real world value use the follow suppositions. Gold in the New Diasporia is worth about US$1000 an ounce. The value of silver to gold is about 15 to 1. With that in mind:
The smallest coin used is the pence. It is about the size and weight of a penny and is made of copper. It is worth the equivalent of ~ 2 cents.
The milli is about the size and weight of a dime, is made of silver and worth about US$2.00.
The spot is about the size and weight of a quarter, is made of silver and worth about US$5.00.
The dime is about the size and weight of a U.S. 50 cent piece, is made of silver and worth about US$10.00.
The Centro is about the size and weight of a dime, is made of gold and worth about US$100.00.
The Quarter Parliament is about the size and weight of a quarter, is made of gold and worth about US$250.00.
The grand is about the size and weight of a quarter, is made of platinum, and worth about US$350.00.
The Parliament is about the size and weight of a U.S. double eagle, is made of gold, and is worth about US$1000.00.
Coins, especially Parliaments, Quarter Parliaments and Centros are sometimes transported in coin socks. The typical sock is made of plastic netting and holds 10 coins.
When moving about large amounts of money it is sometime not convenient to carry around large numbers of coins. As well, in high tech societies it is also very convenient to be able to use electronic money, that is to transfer the ownership of money electronically or using notes or letters of credit.
With this in mind the Highland government does allow the use of banknotes, though it does not issue them. A banknote is a promissory note made by a bank, payable to the bearer on demand for commodity money equal to its face value. The usual issuers of banknotes in the Highlands are banks and credit companies, which sometimes issue loans in the form of banknotes. The Church also issues banknotes, often as letters of credit to its religious and clergy or to pilgrims.
Some other polities in the Midlands and many in the Wilds do issue fiat money. Since it usually has little value outside the particular world or interstellar group most offworlders will not deal in it, preferring strait bartering to holding instruments of dubious value.