Core Mechanics - Fundamentals of Game Design - page 304

Converters
A converter is a mechanic—and usually an entity, too—that turns one or more
resources into another type of resource. In designing a converter, you must specify
its production rate and the input-to-output ratio that governs the relationship of
resources consumed to resources produced. The Settlers offers several examples. The
windmill converts grain into flour at a rate of one to one, so one bag of grain pro-
duces one bag of flour. It takes 20 real-time seconds to turn one bag of grain into
one bag of flour, so the rate of production of flour works out to three bags per min-
ute. The iron smelter turns one load of ore into one iron bar, consuming one load
of coal in the process. However, if fed charcoal instead of coal, the smelter requires
three loads of charcoal for each iron bar because charcoal is less efficient than coal.

Traders
A trader mechanic governs trades of goods, generally between the player and the
game. In a stock-trading game, the trader may be a faceless financial construct; in a
role-playing game, the trader usually comes in the form of a blacksmith who trades
in swords or something similar.

NOTE A trader
is different from a
converter. A trader
changes the ownership
of things, but does
not change the things
themselves. A converter
turns something into
something else, con-
suming the first item
and producing the
second one.

Traders cause no change in the game world other than reassignment of ownership.
If you trade your old dirk and a gold coin for a new short sword, then in theory the
game still contains that dirk, that coin, and that short sword, although all three
articles have been assigned to new owners. The trader can, if your game permits it,
sell the old dirk to the next player who comes along.

THE PROBLEM OF RUNAWAY PROFITS

A player must never be able to repeatedly buy an item from a trader at a low price and
sell it back at a higher price unless you set limits on the process. If players can buy from
and sell to traders indefinitely and rapidly and they can sell something for more than they
paid for it, they will exploit this ruthlessly, piling up huge fortunes by endlessly buying
and reselling and ignoring the rest of the game.

You can use various schemes to prevent this. You can make it impossible to make a profit
by requiring all subsequent sales to be for less than the original purchase price. If you
want players to be able to make a reasonable profit, place limits on the amount of buying
and selling they can do: Require that they wait a while before selling an item back again,
or have the trader refuse to sell items to them more than a certain number of times or
refuse to buy goods back. The trader itself can have limited funds and be unable to buy if
funds run out. In a multiplayer game, you can let players buy and sell at a profit to one
another but not to an automated or NPC trader. Transactions among the players don't
change the total amount of money in the game; but selling things back to an automated
trader mechanic that has an unlimited supply of money has the potential for abuse.