Size does matter, and when it comes to economic heavyweights, the United States heads the pack.
Because of that dominance, the international trade of many commodities takes place in United States dollars, and when the value of that currency moves, so does the value of the commodity when the dollars are repatriated to the seller's currency.
Economists call the US dollar the world's reserve currency.
If the world economy faced uncertainty, many sought sanctuary in US dollars because it was viewed as offering some insulation.
But the risk for exporters was that when the US economy rumbled, as has happened in recent years, the effects were felt via its currency fluctuations throughout the world.
This has been the case for the past five years or so.
Poor performance of the US economy has meant the greenback has also been weak, overvaluing currencies such as the kiwi, making the exchange rate unfavourable to exporters.
The value of the US dollar is influenced by the state of its economy, its current account, business and consumer confidence and how those indexes compare with other economies'.
The key indicators are the level of US inflation, fiscal deficit, interest rates and economic growth. If they are unfavourable, the currency is devalued, as has been the case in recent years.
The New Zealand economy being reliant on exports, the value of the US dollar has been crucial. If it was low, exporters repatriated more money when it was exchanged to New Zealand dollars. If it was high, fewer kiwi dollars ended up in their bank accounts.
Conversely for New Zealand travellers, the weaker the US dollar, the fewer greenbacks they got.
Prospects for sheepmeat farmers this coming season illustrate the relationship between the US dollar and ex-porter incomes.
Meat and Wool New Zealand has calculated that at a NZ dollar-US dollar exchange rate of US70c, farmers would receive $79 a lamb but at US80c, the return would plummet to $67 a head.
In recent weeks, the exchange rate has been below US70c, which, together with soaring demand, helped fuel speculation the price of lamb could be closer to $90.
Exporters also trade in other currencies such as the Euro and the Australian dollar, which can appreciate or depreciate in value according to homeland economic issues, but also to the vagaries of the US economy.
