The earliest form of interval timer was a water clock, which measured the passage of an interval by how long it took water to pass through a hole in the bottom of a vessel.
Many early cultures used these clocks in ancient times, including the "New Kingdom" Egyptians at Thebes
.
The main dial indicates the interval to be timed.
The 24-hour hand (orange) is read against the inner ring of numbers; the minute (blue) and second (red) hands
are read against the large outer numbers.
The subdial on the right is the current time of day.
The subdial on the left indicates the time when the alarm will occur, i.e., the current time plus the interval.
The tiny dot below the 12 on each subdial is black for PM and white for AM.
To time an interval, pull the crown to enter set mode. Then either drag the hands to set the interval, or use the two additional pushers which will appear on the left in set mode: the upper one adds one minute to the interval, and the lower one adds one second. The longest possible interval is 24 hours. The Reset button sets the interval to zero.
The two pushers on the right side are always available. The upper one starts and stops the countdown. The lower one enables the audible sound.
Press the start/stop button to begin the countdown; press it again for a temporary pause. When the count reaches zero, the alarm will sound (if enabled), the indicator will animate and the hands will return to their previous setting. The alarm will ring 20 times (about 10 seconds) or until canceled.
When the alarm is ringing, you can silence it by tapping anywhere on the screen or by shaking the device (note: shaking will not work if the iPhone is locked).
If the iPhone's hardware Ring/Silent switch is set to silent mode, Emerald Chronometer's alarm (when enabled with the pusher) will follow the "Sounds => Silent" setting in the Settings app, either vibrating or doing nothing. If you have Vibrate turned on for "Ring" in that same Settings section, then Emerald Chronometer's alarm will both ring and vibrate.
It is not possible to adjust the main time on this watch.
Note that Istanbul and Thebes are functionally very similar; they both sound an alarm when a target time is reached. The difference is in emphasis: Istanbul focuses on the target time whereas Thebes focuses on the interval. For example, Istanbul's pushers go to even minute boundaries of the target time, whereas Thebes' minute pusher goes to even multiples of interval minutes. There are also subtle differences in the way that time synchronization is handled, to preserve the most accurate interval measurements in Thebes.
If Emerald Chronometer is not running when the target time is reached, and the OS supports it, a local notification popup will be posted (which may play a sound). However, we do not maintain NTP synchronization while in the background (to save battery energy) so the notification may be appear a few seconds early or late.
The alarm will ring if the screen is locked while Emerald Chronometer is running. Unlocking the screen while the alarm is ringing will silence it.
