CLOCK: 24-HOUR TIME
PART OF SERIES, "TRACKING TIME: BEHIND THE CLOCK AND CALENDAR"
Author: Ken Klark L. Flores
Introduction
Clocks come in many styles, from traditional analog designs to modern digital displays, and can be functional pieces for telling time, setting alarms, or serving as decorative home accents (Betts, n.d.).
Origins
This timekeeping evolved over millennia from ancient natural indicators to modern atomic precision, with the term "clock" deriving from the medieval Latin word clocca, meaning 'bell', as early mechanical clocks primarily signaled time with sound (Bellis, 2019).
Among the oldest timekeeping devices, ancient Egyptian obelisks and shadow clocks, dating as far back as 3500 BC, used the sun's shadow to divide the day. They were, however, useless at night or on cloudy days. That's the principle of Sun Dial Clocks (Hepler, 2019). Water Clocks (Clepsydras) are possibly the oldest time-measuring instruments not based on astronomical observation (after tally sticks), these used the regulated flow of water to measure time intervals. Bowl-shaped outflow water clocks existed in Babylon and Egypt around the 16th century BC. The Greeks and Romans later advanced their design to include gears, dials, and even early alarm mechanisms.
The major shift occurred with the invention of the mechanical clock in Europe around the late 13th and early 14th centuries. These weight-driven clocks used an oscillating mechanism, known as an escapement, to control the release of power, making accurate, consistent timekeeping possible in all weather conditions (First Mechanical Clock | EBSCO, 2022). First Mechanical Clocks are placed in cathedrals and priories in their clock towers, primarily to signal times for prayers and public events by striking bells. The invention of the pendulum clock by Christiaan Huygens in 1656 dramatically increased accuracy. Subsequent innovations, such as the balance spring, enabled the development of accurate portable clocks and watches (Seiko, n.d.).
Modern Timekeeping made further technological advancements of clocks. Electric Clocks are patented in 1840 by Alexander Bain, these used electricity to sustain the pendulum's motion or wind the spring. Quartz Clocks, like used in our everyday lives, which powered by an A or AA or AAA Battery, is developed in 1927 by Warren Marrison and J.W. Horton at Bell Telephone Laboratories, these rely on the precise, regular vibrations of a quartz crystal in an electrical circuit, becoming the dominant timekeeping technology due to their low cost and high accuracy (The Complete History of Mid-Century Modern Clocks - by Royale, 2025).
The most accurate clocks in existence, atomic clocks use the constant frequency of electron transitions in atoms (like caesium) to define the second. The first practical atomic clock was built in 1955 by Louis Essen, and they are now the international standard for timekeeping.
Two primary numeric time notation systems
The day is divided into two 12-hour periods, designated a.m. (ante meridiem, "before midday") and p.m. (post meridiem, "after midday"). This system is commonly used in several English-speaking countries, including the United States, India, and Australia (12-Hour Clock | Description, History, and Facts | Britannica, n.d.). The day runs from midnight to midnight, with hours numbered from 00 to 23 (or 24 to indicate the end of a day). This system is the international standard (ISO 8601) and is widely used globally, especially in professional fields like aviation and medicine, to prevent ambiguity (Costa, 2025).
Synchronization
In institutional and commercial settings, a clock network ensures all clocks show the exact same time.
These systems consist of a master clock that receives an accurate time source (e.g., via GPS or Network Time Protocol (NTP) servers) and one or more connected slave clocks (wired, wireless, Wi-Fi, or Power over Ethernet) that display the synchronized time (Introduction to Clock Systems | National Time & Signal, 2025).
Time Zones
A time zone is a region of the globe that observes a uniform standard time for legal, commercial, and social purposes. This system coordinates time with daylight by dividing the Earth into segments based on its rotation, primarily using the Coordinated Universal Time (UTC) offset as a reference (Time Zone, n.d.).
The Earth rotates 360 degrees in 24 hours, meaning it turns 15 degrees of longitude every hour. In theory, there are 24 time zones, each 15 degrees wide. Every time zone is defined by its difference from Coordinated Universal Time (UTC), which is based on the Prime Meridian (0° longitude) in Greenwich, London. Offsets are expressed as UTC- or UTC+, followed by the number of hours and minutes (e.g., the Philippines is UTC+08:00).
Time zones originated in the late 19th century as a solution to scheduling chaos caused by the rise of rapid railway transportation. Before this, most towns and cities set their clocks locally based on the sun's position, resulting in hundreds of different "local solar times"(kozeck, 2022). In 1884, the United States helped convene the International Meridian Conference in Washington D.C., where delegates from 25 nations agreed to adopt a single Prime Meridian passing through the Royal Observatory in Greenwich, England. This established Greenwich Mean Time (GMT) as the international standard from which all other time zones would be referenced (M. A. & B. A., n.d.).
Many regions observe Daylight Saving Time (DST), a practice where clocks are typically advanced by one hour during spring and summer months to make better use of natural daylight. Areas that use DST have two different time zone names and offsets throughout the year (e.g., Pacific Standard Time (PST) is UTC-8, while Pacific Daylight Time (PDT) is UTC-7). Most of Arizona and Hawaii in the US do not observe DST (Buckle, 2019).
Reference
Betts, J. (n.d.). Clock | measurement device. Encyclopedia Britannica. https://www.britannica.com/technology/clock
Bellis, M. (2019, February 6). Who Invented the Clock? ThoughtCo; ThoughtCo. https://www.thoughtco.com/clock-and-calendar-history-1991475
Hepler, R. (2019). The Invention and Impact of Mechanical Clocks - Video & Lesson Transcript | Study.com. Study.com. https://study.com/academy/lesson/clocks-history-of-chronometers-and-mechanical-clocks.html
First Mechanical Clock | EBSCO. (2022). EBSCO Information Services, Inc. | Www.ebsco.com. https://www.ebsco.com/research-starters/history/first-mechanical-clock
Seiko. (n.d.). First-ever mechanical clock. THE SEIKO MUSEUM. https://museum.seiko.co.jp/en/knowledge/MechanicalTimepieces01/
The Complete History of Mid-Century Modern Clocks - By Royale. (2025, March 13). By Royale. https://by-royale.com/history-of-mid-century-modern-clocks/
12-hour clock | Description, History, and Facts | Britannica. (n.d.). Www.britannica.com. https://www.britannica.com/topic/12-hour-clock
Costa, D. (2025). 24-hour clock | Definition, History, Uses, & Facts | Britannica. Www.britannica.com. https://www.britannica.com/topic/24-hour-clock
Introduction to Clock Systems | National Time & Signal. (2025, September 2). National Time & Signal. https://www.natsco.net/clock-systems/introclocksystems/
Time zone. (n.d.). Encyclopedia Britannica. https://www.britannica.com/science/time-zone
kozeck. (2022, August 4). Who Created Time Zones? | The Franklin Institute. Fi.edu. https://fi.edu/en/blog/who-created-time-zones
M. A., G., & B. A., G. (n.d.). How Long Have We Had Time Zones? ThoughtCo. https://www.thoughtco.com/what-are-time-zones-1435358
Buckle, A. (2019). What Is a Time Zone? Timeanddate.com. https://www.timeanddate.com/time/time-zones.html
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