"Clock time is a fungible measure of sacrifice. Of all measurement instruments, the clock is the most valuable because so many of the things we sacrifice to create are not fungible. The massive clock towers of Europe, with their enormous loud and resonant bells, broadcasting time fairly across the town and even the countryside, rather than the last relics of the medieval, were the first building block of the wealthy modern world. The Europeans evolved their institutions and deployed two very different but complementary timekeeping devices, the sandglass and the mechanical clock, to partition the day into frequently rung and equal hours. Europe progressed in a virtuous circle where bells and clocks improved the productivity of relationships; the resulting wealthy institutions in turn funded more advances in timekeeping... The massive change on the farm, the dominant form of industry, in the 14th and successive centuries from serfdom and slavery to markets and wage labor, was caused not only by the temporary labor shortages of the Black Plague, but more fundamentally and permanently by the time-rate contract and the new ability to accurately and fairly verify its crucial measurement of sacrifice, time. Time rates also became the most common relationship for the mines, mills, factories, and other industries that rapidly grew after the advent of the clock."