The Milliways principle is one of the most ingenious inventions of the banking industry, second only to compounding interest, free toasters with a new account, and those little windows that close when someone wanting money approaches (this latter invention has totally revolutionized life on Al-Deneb VI, where it is considered extremely rude to refuse to lend a friend a few Altairian dollars -- even if the ungrateful bastard has already touched you fifty times in the past week for more than your annual income and has no job and no prospect of getting a job because no employer will see him because they're afraid he'll ask for a seven-year advance in his salary even tho' he hasn't been hired yet and they'll be forced to give it to him because it would be rude not to -- on Al-Deneb VI they carry these windows around in front of them wherever they go -- it saves them a lot of money -- even taking into account the royalties they pay to the banks).
The Milliways principle is named for Milliways restaurant. In order to pay the outrageous rates that eatery charges, the patrons deposit one penny in a bank in their own time period. The tab is paid from the interest built up over the trillions of years that penny sits in the bank. When Milliways comes to collect, the bank charges a service fee amounting to several percent of the charge -- usually just enough to empty out the account. Both the bank and the restaurant then use TFT (Temporal Funds Transfer) to take their profit back to some time when there were still things to buy with their fabulous wealth.
(OK, so when you count them up, the Milliways principle is the fifth most ingenious idea that the banking industry has come up with. I never claimed to be very good at this counting stuff. On my accountant's advice I leave that to her.)
- Galactic Postal Service