In the history of watchmaking, how was the interval of a second agreed upon?

Tizzabelle

http://en.wikipedia.org/wiki/Units_of_time "The introduction of the minute (minuta) as the 60th part of an hour, the second (seccunda) as the 60th part of a minute, and the third (tertia) as the 60th part of the second dates to the medieval period, used by Al-Biruni around AD 1000, and by Roger Bacon in the 13th century. Bacon further subdivided the tertia into a quarta or fourth. Hindu chronology divides the civil day (daylight hours) into vipalas, palas and ghatikas. A tithi is the 30th part of the synodic month." Dec 09 11, 1:32 PM