ratio

比価　—　Measuring

The rate of exchange between two metals, such as gold and silver.

Noble of Edward III1344– GuineaAD 1663–1814 Draped Bust dollarDated 1796

Even in the same period, the bimetallic ratio differed from country to country. When it differed, people would appear who bought in the cheaper market and sold in the dearer one, and one of the metals would flow out of the country. This is usually how bimetallism collapses.