摩尔分数或比率，但它是有单位的。
1999年1月1日11个国家的货币跟一种新货币，即欧元的比率固定下来，欧元也成为批发金融市场中的结算单位。
On January 1st 1999 the currencies of 11 countries were fixed against a new currency, the euro, which became the unit of reckoning in wholesale financial markets.
确定测量单位——以测量的术语来表达控制对象，如数量、比率、指数、权数等等。
Define a unit of measure - express the control subject in measurable terms such as quantities, ratios, indices, rating etc.
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