In order to the immediate detection of an alteration in the course of exchange, it was desirable to have a certain fixed point of calculation to which all variations might be referred. This fixed point was called the par of the exchange, and denoted, when it was first instituted, a perfect equality of exchange, both of goods and money, between the trading parties. The exchange between Holland and Great Britain was at par when the two countries sent exactly the same amount of wealth to each other. Supposing ten guilders to go to a pound, the exchange would be at par when the Dutch exported to England one thousand guilders' worth of commodities, and imported from England one hundred pounds' worth of commodities. So that, so long as ten guilders go to a pound, and Holland and England exchange the same quantity of goods, the exchange will not vary, really or seemingly, from the fixed point of calculation. It is only the one country exporting more goods than the other which can really make the amount of value due greater from one than the other: but, because ten guilders have not always gone to a pound, more money has sometimes appeared to be due from one than the other, even while the quantity of goods exchanged has been precisely the same, as computed in anything but the altered money. When eleven guilders go to the pound, while the par of exchange is still called ten, more money will appear to be due from Holland to England for the same quantity of goods as before; and consequently, while the actual state of trade will be exactly the same as before, it will be declared on 'Change that the exchange has turned against Holland; _i. e._, that Holland owes more money to England than she has to receive. However, merchants whose interest it is to watch the course of exchange, easily distinguish the real from the nominal variation, and learn to make use of the fixed point of calculation with due allowance for the difference caused by the alterations in the value of money. They can ascertain what they want to know of the general state of commerce, in the midst of what would be, to an inexperienced person, a deception; and a merchant who has, by any rare accident, been prevented from going on 'Change, only wants to know the nominal variation from par, and to compare it with his knowledge of the respective currencies of the two countries, to satisfy himself as to which ought to push its exports, and which its imports.