being the one after dawn, to having the hour after noon being designated as 1 pm (post meridiem), is that these clocks would likely regularly be reset at local high noon each day. This, of course, results in midnight becoming 12 o'clock. Peter Henlein, a locksmith and burgher of Nuremberg, Germany, invented a spring-powered clock around 1510. It had only one hand, had no glass cover, and was rather imprecise because it slowed down as the spring unwound. In fact, Henlein went so far as to develop the first portable watch; it was six inches high. People usually carried it by hand, or wore it around their necks or in large pockets. The first reported person to actually wear a watch on the wrist was the French mathematician and philosopher, Blaise Pascal (1623–1662). He attached his pocket watch to his wrist with a piece of string. In 1577, the minute hand was added by a Swiss clock maker, Jost Burgi (who also is a contender for the invention of logarithms), and was incorporated into a clock Burgi made for astronomer Tycho Brahe, who had a need for more accuracy as he charted the heavens. Isochronous time With invention of the pendulum clock in 1656 by Christiaan Huygens, came isochronous time, with a fixed pace of 3600 seconds per hour. By 1680, both a minute hand and then a second hand were added. Some of the first of these had a separate dial for the minute hand (turning counter-clockwise), and a second hand that took 5 minutes per cycle. Even as late as 1773, towns were content to order clocks without minute hands. But the clocks were still aligned with the local noonday sun. Following the invention of the locomotive in 1830, time had to be synchronized across vast distances in order to organize the train schedules. This eventually led to the development of time zones, and, thus, global isochronous time. These time changes were not accepted everywhere right away, because many people's lives were still tied closely to the length of the daytime. With the invention in 1879 of the light bulb, that changed too. The isochronous clock changed lives. Appointments are rarely "within the hour," but at quarter hours (and being five minutes late is often considered being tardy). People often eat, drink, sleep, and even go to the bathroom in adherence to some time-dependent schedule. See also 12-hour