how did the persians keep track of time?
By using water clocks
History of timekeeping devices
According to Callisthenes, the Persians were using water clocks in 328 to ensure a just and exact distribution of water from qanats to their shareholders for agricultural irrigation. 
who invented the first mechanical clock in 1300 Catholic monks which of the earliest civilizations used timekeeping devices? Hunter-gatherers, Prehistoric Europe, Mesoamericans, etc why did the monks invent the clock? To regulate daily prayer- and work-schedules strictly and to ensure accuracy can you give me examples of timekeeping devices? Astronomical bodies, sticks and bones to track the phases of the moon or the seasons, Stone circles, sexagesimal timekeeping, and vigesimal counting system name some of the innovations during the medieval period Clock, wristwatches, Clock of the Long Now, mechanical clock, and pendulum clock did ancient egypt use timekeeping devices? Yes, Shadow clocks and Sundials what about greece? They used water clocks, or clepsydrae, and water-based alarm clock name some of the innovations during the pre-modern period Mechanical clocks and pendulum clock is it possible to keep track of time underwater? Yes, by Marine chronometers
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History of timekeeping devices [SEP] Ancient and medieval Persia
According to Callisthenes, the Persians were using water clocks in 328 to ensure a just and exact distribution of water from qanats to their shareholders for agricultural irrigation. The use of water clocks in Iran, especially in Zeebad, dates back to 500. Later they were also used to determine the exact holy days of pre-Islamic religions, such as the "Nowruz", "Chelah", or "Yaldā"—the shortest, longest, and equal-length days and nights of the years. The water clocks used in Iran were one of the most practical ancient tools for timing the yearly calendar. Water clocks, or "Fenjaan", in Persia reached a level of accuracy comparable to today's standards of timekeeping.