Emerald Chronometer HD is a watch simulator app for the iPad made by Emerald Sequoia. (There’s an iPhone version too, called Emerald Chronometer.) The app consists of fifteen watches (named after cities) created in software, with each watch offering different features on its front and rear faces.
At first glance, you might imagine that there’s not much point to simulating watches on an iPad. After all, doesn’t the iPad tell the time perfectly well, even if it doesn’t come with a built-in clock app, like its smaller brother?
But you’d be wrong: the developers of Emerald Chronometer have blended the legacy of centuries of fine watch-making craftsmanship with the latest interactive touch-screen technology to build a digital playground that lets you investigate the worlds of time-keeping and astronomy with your fingertips.

Each ‘watch’ offers a different approach to time. Rather than copy existing models, the designers have created new, imaginary watches that blend features from traditional time-pieces with features that you could expect to find only on an extremely expensive watch, or a powerful computer.
For example, the Vienna offers a traditional 24-hour display (the rear face offers a version with 12 at the top). The app synchronizes with the NTP protocol over the internet, which means that these watches almost certainly keep time more accurately than the iPad itself. I’ve clicked on the Time Synch button which pops up a display showing how far adrift my iPad is. The white, black, and grey bands on this and other watches show the current lengths of day, night, and moonlight periods.

Where the Vienna is simple, the Geneva is complex. The front face shows the time as fully as possible, including years and leap years (recognizing both Julian and Greogrian calendars), sun and moon rising and setting times, and moon phase and age. The rear face shows local apparent sidereal time on a 24-hour dial, the zodiac, equinoxes, and solstices, the positions of the lunar ascending and descending nodes – even whether there’s an eclipse soon.

But the real magic of this app is revealed when you ‘pull out’ (or tap) the crown for the current watch. The watch stops, and you can then pull and push the hands and indicators around the dial to your heart’s content. Watchmakers will find it unbearably painful to look at as you pull the hour and minute hands into different positions, or scroll the indicator dials up and down through the years with the flick of a finger. If, as you’re moving through time, there’s the possibility of an solar or lunar eclipse, the eclipse indicator at the top of the Geneva will let you know.
The Alexandria watch, named for Ptolemy’s home town, displays the time using a geocentric display; the Firenze watch, named for Galileo’s sometime home, is an orrery – a sun-centered display of the solar system. And in each case, you can drag the planets around to see how they move in space as you travel through time.

The Miami watch shows the rise, transit, and set times of all the planets (and the Sun and Moon), with a single hand on a 24-hour dial, and their current azimuth and altitude.

The Terra watch specializes in time zones: the front shows your chosen zone at the top, with a 24-hour ring to help you read off the time in other cities. Again, being able to move the rings round makes it easy to explore time zones and time differences. The rear face provides four dials for your favourite cities.

On the Olympia, you’ll find a stopwatch; on the Thebes, a countdown timer; and on the Istanbul, an alarm, which chimes like a traditional watch.
If you have an iPad (or an iPhone), this app is a cool and clever addition to your library, and a pleasant way to spend (and learn about) time.