The combination of commodity and currency qualities of gold is its main advantage, allowing this precious metal to be used as a universal means of payment for all market participants. The gold standard is a monetary system in which the basic unit of account is a certain standardized amount of gold. One troy ounce of gold, equal to 31.1 grams, is taken as the basis of the gold standard (investment gold). The invoice price or contract price is fixed not in currency, but in grams, kilograms, or ounces of gold.