Craig Duling's fascination with timepieces goes back at least to his college days, when he built a digital clock from scratch for his senior year physics lab class. Currently the head of Heritage Management Services, a business management firm in San Francisco, Craig Duling is also a significant collector of rare antique pocket watches. Pocket watches are often associated with images of 19th-century railroad conductors consulting them as steam trains left the station. This close attention to correct time was essential. In the 19th century, most trains traveled in both directions on single sets of tracks. Sidings were placed at regular intervals to allow trains to pass safely. Printed timetables showed the arrival and departure of trains, as well as when they were waiting in sidings. This system depended on accurate watches. The problem with this became evident in 1891 when two trains in Ohio had a head-on collision, killing nine people. Investigation disclosed that the engineer's watch on the passenger train had stopped and restarted, making it four minutes slow. This tragedy prompted railroad officials to set up standards for pocket watches. These specifications mandated that watches share a common design, as well as being reliable, easy to read, and impervious to extremes of temperature.