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Emerald Chronometer Options

Emerald Chronometer's settings and options are accessed via the "gear" button in the lower right corner of the screen. There are global app options relating to time synchronization, geographic position, and screen auto-lock. Following those are settings specific to a single watch. Currently only Terra has any watch-specific settings. See Terra's Help page for a description of those settings.


Emerald Chronometer does not depend entirely on the iPhone's internal time, which is frequently off by several seconds and can change abruptly as it contacts different cell phone towers. This can be avoided, if you have Internet access, by using this option:
ntp setting
This tells Emerald Chronometer to synchronize its time using the Network Time Protocol (NTP). The NTP time is stable and usually differs from the international standard atomic clocks by less than a few hundred milliseconds. The indicator light will blink during the sync process (it can take some time if the network is flakey). For a technical description of what Emerald Chronometer does during synchronization, click here. "Use NTP" is ON by default.

When all else fails, you can set the date and time and time zone manually with the Settings App: Settings -> General -> Date & Time.

Emerald Chronometer uses the Gregorian calendar for future dates and for past dates back to 1582, and the Julian calendar from 1 BCE to 1582 CE. Prior to 1 BCE Emerald Chronometer uses a proleptic Julian calendar, with leap years on 1BCE, 5BCE, etc, back every four years. Until very recently calendar representations around the world have varied widely, so using Emerald Chronometer for actual historical dates requires an advanced knowledge of Chronology (far beyond the scope of this note).

Click here for a description of the accuracy of Emerald Chronometer's astronomical calculations.

Geographic Position

You set the geographic location and timezone with these two options:
position entry
The right hand side labels indicate the current settings; the text is blue if the item is set automatically, purple if set manually. Tapping them brings up the screens described below.

Most astronomical calculations depend on your position on the Earth's surface. So Emerald Chronometer has a number of ways to for you to specify a position; they are accessed via the locations options screen:

location screen
And the time displays depend on the timezone which you can specify via Emerald Chronometer's timezone setting screen:
timezone screen

By far the most important aspect of each of these are the switches at the top. If they're both set to "ON" then your position and timezone will be determined automatically and in most cases that will be sufficient and you can stop reading now. They are both ON by default. See below for a description of how these automatic determinations are made. When the switches are ON the rest of the screen is a read-only display. Since location and timezone are closely related the bottom section of the location screen shows the timezone that is currently in effect; it is always read-only.

Manual location setting

If you turn the "Use Device Location" switch OFF the screen changes to the manual setting form:
manual location screen

Here you can set your location by entering a city name, by choosing a city from your Contacts list, by entering latitude and longitude values, by scrolling the map, or by picking a previously used location:

Manual Timezone setting

First note that if you have set your location manually as described above, there is usually no need to set the timezone manually; it will automatically pick up the timezone of the chosen location in most cases.

If you turn the "Set Automatically" switch OFF the timezone setting screen changes to its manual entry form:

manual timezone setting
This is a two-level view of the world's 400+ timezones. 18 of the most commonly used zones are listed under the first entry; otherwise first pick a continent then pick a city from the ensuing list. A few non-standard but often seen timezones are listed in the last entry ("Other"). The currently chosen timezone will appear to the right of its continent name; timezones with the same UTC offset as the currently chosen one will be shown in blue.

If you pick a timezone that doesn't seem to match your current location a warning box will appear. The same warning will appear if you choose a seemingly inappropriate location while the timezone is set manually. This is just a warning, Emerald Chronometer will honor your choice. But be sure you know what you're doing if you see it. Some of Emerald Chronometer's displays will be incorrect (or look very odd) if your location and timezone do not match (eg, if you're in New York City but you set your longitude to "74" instead of "-74"). If you change either one manually make sure the other one is consistent. If you allow both to be set automatically then everything is usually OK.


Turning on one of these options overrides the iPhone's normal Auto-Lock setting (in Settings->General) so that Emerald Chronometer's display will remain active indefinitely. There are two settings, one which controls what happens when the phone is plugged into a power source, and a second which controls what happens when the phone is running on battery power:
auto-lock setting
Warning: If the second option is enabled, this will drain the battery in just a few hours.

This option applies only when Emerald Chronometer is running; it has no effect on other apps.

Auto location

Emerald Chronometer uses the iPhone's "Location Services" to get the geographic location it needs in order to calculate the times of astronomical events like sunrise and sunset. Location Services uses a variety of methods to determine location depending on the available hardware including GPS, cell phone tower triangulation and a database of WiFi hotspots.

Emerald Chronometer will start up assuming the same timezone and location settings as it had the last time it was run. It may then take up to a minute or so to get an accurate location fix. The location status indicator will blink during this process. If Emerald Chronometer is running when the fix is determined then the affected watch hands will move to the correct positions.

To use Location Services, you must enable it in the General section of the Settings app AND set "Use Device Location" to "ON" in the locations screen.

In order to save battery energy, Emerald Chronometer asks for its location only at startup and at 30-minute intervals. If you are in a fast-moving vehicle and want the utmost accuracy in the astronomical displays, you can force another location update by entering the location setting screen again. You can see it move in real time with the big map.

The algorithm used to determine the timezone when the "Set Automatically" switch is ON is based on the setting of the "Use Device Location" switch. If it is also ON then Emerald Chronometer just uses the timezone from iPhone OS. This is in turn based on the settings in Settings->General->Date & Time; when set to "Set Automatically" the timezone is received from the cell phone network (which is not always right). If Emerald Chronometer is in manual location mode, the auto-timezone is taken from our internal database.

Devices without GPS

The some iOS devices do not have GPS or cell phone triangulation or cell phone time synchronization. But they do have WiFi. If you take such a device to a "well-known" WiFi hot spot, and start up Emerald Chronometer there with "Use Device Location" ON, then it will remember that location and use it until you uninstall the application or start it up in another well-known location. Devices running iPhoneOS versions prior 3.2 use the "SkyHook" database of well-known locations; you may be able to find one using SkyHook's locator. You can even (if you're willing to wait for them to update their database) enter your own WiFi access point. Devices running iOS 3.2 or newer use Apple's database.

The Watches

Copyright © 2009, 2010, Emerald Sequoia LLC; last updated: 2010 April 20

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