如果米、克和秒保持不变，为什么美元却一直在变化？前者是对稳定物理量的度量，而后者是一种“伪度量”，即它被当作度量来使用，但目前无法将任何稳定的物理量正确地归于它。由于货币目前并不以任何稳定、有形之物作为后盾，大量聪明人（为了不错过这些利益）把时间用在追随货币市场的舞步上。他们并不把它视为问题，而是视为赚取更多利润的机会。有人通过预测下一步走势来获利，也有人试图亲自编排这场舞蹈本身。 货币或金钱是一种价值单位。换言之，某种商品或服务与货币的交换比率被称为其“价格”。值得注意的是，“交换价值”或通常所说的“价值”，是一物与另一物交换的比率，因此价格也是一种交换。但与一物换另一物的交换不同，所有事物的价格可能在同一时间同时上涨或下跌。因此，某物的价格只是它的诸多价值之一。如果货币以某种稳定、有形之物固定其价值（例如1单位货币 = 1克黄金），它确实就会像米或秒一样成为一种度量。 一千多年来，货币都以某种标准为基础（如金本位），并持续作为交换媒介，因此对大多数普通人而言，货币通常被理解为衡量事物价值的度量。然而，这种以稳定、有形之物为标准的做法在20世纪后期已不再存在，货币因而被视为一种单纯的物品，只具有名义上或暂时的价值。货币的名义价值未必以其与其他商品或服务的真实交换比率为基础；事实上，它后来仅仅基于人们或交易者的认知。

If the metre, gram and second remain constant, why does the dollar keep changing? The former units are measures of stable physical quantities, while the latter is a pseudo-measure, i.e. it is used as a measure but currently no stable physical quantity can be correctly attributed to it. But as currency is currently not backed by something stable and tangible, significant numbers of bright people (not to lose out on the spoils) devote their time following the dance of the currency markets. Rather than considering it a problem, they see it as an opportunity to generate more profit. Some make profits by predicting the next move while some try to actually choreograph the dance itself. Currency or money is a unit of value. In other words, the exchange ratio of a product/service with money is called its ‘price’. It is noteworthy that the ‘value of exchange’ or ‘value’ as it is usually called, is the ratio of an exchange of one thing with another, and price therefore is a type of exchange. But unlike exchanges of one thing with another, it is possible that the prices of all things rise or fall at any one time. Hence the price of a thing is merely one of its values. If money had a fixed value in terms of something stable and tangible (for example 1 unit of money = 1g of gold), it would indeed be a measure, like the metre or the second. For more than a millennium money was based on some standard (like the gold standard) and it continued to be the medium of exchange, and hence for most ordinary people money is commonly understood to be a measure of the value of things. But that standardisation to something as stable and tangible, ceased to be the case in the latter part of the 20th century, and as such money came to be considered a mere object, which only has a notional or temporal value. The notional value of money may not necessarily be based on real exchange ratios with other commodities or services; in fact it came to be based merely on the perception of people or traders.

因此,商品或服务的价格或价值,随货币的名义价值波动,其波动幅度甚至可能超过商品或服务本身的重要性或效用,即"效用价值"。遗憾的是,这正是当今世界衡量价值的方式。因此,你的房产价值上涨或下跌也就不足为奇了;一个多世纪以来,每隔十年左右就会出现一次繁荣与萧条的讨论,这种情况已持续了一百五十多年。

So, the price or value of things fluctuates according to the notional value of money, as much or even more than the importance or benefit of the product or service, or the ‘value of benefit’. This is unfortunately how things are valued in today’s world – hence it is not surprising to find the value of your house rising and falling, and for over a century there has been talk about boom and bust at least once every decade for over 150 years.