Nails themselves have changed over the years, but Sichel studied them because they haven't changed much.

钉子本身随着时间的推移而变化，但西切尔之所以研究它们，是因为它们变化不大。

The price of nails fell by 90% between the late 1700s and mid-1900s, as Daniel Sichel points out in a research paper.

如丹尼尔·西切尔在一篇研究论文中指出的，从18世纪末到19世纪中期，钉子的价格下降了90%。

According to Sichel, although the falling price of nails was driven partly by cheaper iron and cheaper energy, most of the credit goes to nail manufacturers who simply found more efficient ways to turn steel into nails.

根据西切尔的说法，尽管钉子价格的下降部分是由于铁和能源的价格下降，但大部分功劳应归功于钉子制造商简单地找到了更高效的将钢转化为钉子的方法。