Rewards programs also seem to offer a lot, but the card holder gives up much in return.

FORBES: Card Sharks

Holyrood's out-going presiding officer, Tory, Alex Fergusson, will be the first former holder of the post to return to parliament as an MSP.

BBC: Scottish election: Labour MSP in presiding officer bid

Broadly, instead of using simple supply and demand, it explains changes in the demand for one asset (a small silver coin, say) relative to another (a large coin) in terms of changes in the rate of return that the holder of the assets can expect from each.

ECONOMIST: The lessons of sound money from 1,000 years' experience