The process ends with the exchange of items and can be considered as consisting of two item transfers. The important aspect of barter is a desire to exchange. Value is the ratio in which the unit of measure of one thing exchanges for a multiple, or fraction, of the unit of measure of any other determinate thing. Thus, for instance, we may say that the value of a certain kind of wheat, at a given time and place, is thirty shillings, if a quarter of such wheat is actually exchanged, at that time and place, for thirty shillings. Value, in other words, is a mathematical proportion between two quantities of wealth exchanged against one another in a given market.
Agents assign values to items according to different criteria.
One other criterion that decides the value is the time and place the barter takes place. If an item is not produced or easily found in a country, then its value is greater than the same kind of item's value where it is produced. As a result, value is effected by many factors such as economical, psychological, historical, etc. Such match-ups scarcely exist in the real world.