Emerald Timestamp lets you capture the precise times of events, and associate a description with each one. It's a universal app which runs at full resolution on the iPad, iPhone, and iPod touch.
Press the large button with the arrows pointing down to record the current time value. It will show up at the top of the list below. Add as many as you like; the list scrolls.
To add a one-line description, tap an event in the list and enter the description on the detail page (see below).
Tap the date or time at the top of either screen to change the format of the time displays. Each tap cycles between 12-hour local, 24-hour local, UTC (aka GMT), Julian Date (an astronomical time reference; see below), and "interval" times (see below). You can choose a subset of these time formats to be cycled through using the Options panel (see below).
To find the difference in times between events, switch to "interval" display (see above) and then tap the "zero" button on an event in the list, and other times will be measured against that zero reference. Equivalently, press the "Use as reference zero" button on the detail page for an event. The behavior is different depending on whether the option "Allow multiple interval zeroes" is turned on (see below):
Options (Settings) are available via the Options button at the bottom center. On the Options screens you can
The iPhone's internal clock can be somewhat unreliable. So when Emerald Timestamp starts up (and every time it is awakened after the device has been locked) it uses NTP to synchronize its own clock with the international standard atomic clocks. This process requires network access and can take several seconds. Until it is done the accuracy of event timing is somewhat uncertain. During that uncertain time, Emerald Timestamp's big button is yellow. When the sync is complete, the button turns green and event timing is very accurate.
Emerald Timestamp uses location services to determine the best time servers to contact. Time servers that are in the same country will generally result in faster round-trip times and thus better accuracy and faster synchronization.
You can record events even when the button is yellow. If a sync is completed before the app is shut down or the device is locked, then the sync will be applied retroactively to all events captured since the last startup or unlock (and the displayed time values for such events may change as a result). The green/yellow indicator light to the left of each event indicates its time accuracy.
Tapping an event in the list brings up a page showing more detail about that event. You can add a one-line description by tapping the "Event description" field. You can email this event's details or the details of all the events.
The detail page also shows an accuracy bound for the time of the event. The accuracy of synchronized events is primarily constrained by the length of time it takes for a round trip from the device to the NTP server and back; server times are usually much more accurate than that round-trip time. Emerald Timestamp reports the accuracy based on that round-trip time, refined by a number of request-report cycles, and including an estimate of the server error based on its own reported parameters.
A synchronization is considered "green" by default if its reported accuracy is less than 0.40 seconds; this threshold may be set in Settings (see above). In "interval" mode (see above) both events must have an accuracy less than the specified accuracy for the interval to be green; the detail page reports the actual combined accuracy (which may not be larger than an individual event's accuracy if the app session was running continuously between the two events). Regardless of the threshold chosen, Emerald Timestamp continues to refine the synchronization until the error is no more than 0.16 seconds, or until it times out trying (after a minute or two).
At the top right of the main screen is an indicator of the current accuracy bound. It's gray while synchronizing, and white at other times. Tap it to force another synchronization.
Press the Edit button in the lower right to remove one or more events from the list. The button at the lower left starts out as "Delete All", which will remove all events at once; or you can tap individual events to select them and then tap the lower-left button, which will be labeled "Delete (n)" where n is the number of events that will be deleted.
This version of Emerald Timestamp has tentative support for live leap-second display. See this page for details.