Now that Arc Diem is released for both Pebble and Garmin--that is, now that I've had the experience of making a watchface for both platforms--now is a good time to share my thoughts on the different philosophies behind these watches, and how that affects the experience of developing for them and what features go naturally with different watches.

First, the Pebble. EOL aside, it's easier for me to write if I keep this in the present tense.

Pebble's first priority is to be a good watch that gains very open-ended functionality when able to communicate with a smartphone. Accordingly, it has only a few sensors of its own--just a timer, and an accelerometer that tracks wrist movement. (Unless you were lucky enough to get a Pebble 2 HR; then you also get a heart rate sensor.) It prioritizes long battery life and functionality. Pebble knows that it doesn't have to be a full wrist computer; it just has to provide its users with the ability to put their few favorite functions on a super easy-to-reach button and display. This means providing an easy-to-use development platform, so that it's easy for users to develop exactly what they need. For a Pebble, it's okay to have a black-and-white display if that means a longer battery life, as long as function is not compromised.

Garmin predates smartwatches. They got their start making GPS devices, like in-car navigation before phone-and-Google-maps became standard issue. They also make cycling computers that you can attach to your bike; these not only act as speedometers, but can also track things like cadence (how fast you move the pedals around) and what gears you're using, that require the bike itself to have sensors attached. So a move into smartwatches was a logical next step.

This leads to one large hardware difference between Pebbles and Garmins: all Garmin watches have built-in GPS. Watchfaces are not allowed to invoke it directly, so as not to drain the battery too fast, but the watch does remember its last known location for a few hours. Accordingly, Garmin provides easy functions to access the GPS data, either by calling GPS directly (for an app or widget, which are allowed to drain the battery more) or by checking the last known location (for watchfaces, or anything else willing to sacrifice accuracy for battery life).

Pebbles can use GPS as well, but they have no internal sensors for it: in order to get GPS data, they must communicate with their connected smartphones. So accessing GPS with a Pebble requires going through the "communicate with the phone" API, which is more complicated than just calling a provided GPS method.

What this means for watchfaces is that it's relatively easy to provide the local times of sunrise and sunset on a Garmin watch. Many Garmin users love having this data on their watchface; some consider it essential. So, many watchfaces in the Garmin app store provide this data (at least, as best they can, considering the GPS limitation on watchfaces). Arc Diem's design naturally lends itself to using sunrise and sunset as dial boundaries, so on a Garmin, I felt motivated to include this function (and moon phase as well, which is much easier to calculate), while on a Pebble it wasn't worth the effort of including.

Step counting is another function that is baked into Garmin watches. Anyone who gets a Garmin watch is prompted, when setting it up for the first time, to specify some daily step goal. The watch always tracks the wearer's steps taken each day, and accordingly provides easy functions to access the step count and goal. This makes it very easy to include step data on a watchface, and again, since Garmin users tend to be sports-and-fitness-oriented, they tend to like having that data visible. On a Pebble, step counting is not a built-in feature; it requires the assistance of a dedicated app that calculates steps from the accelerometer data.

Then there's heart rate. Not all Garmin watches have built-in heart rate sensors, but they do all have the capability to pair easily with other devices that measure it, like chest straps. Even people who use sensor-equipped watches might prefer to get data from a chest strap when actually training, because data from a chest strap tends to be more accurate than data from the wrist. Therefore, Garmin provides easy-to-use functions that get heart rate data from any source that is available. Pebble may have added this in their later stages, considering the presence of an HR sensor in their last watch, but it was never a core feature as it is with Garmin watches. Again, many Garmin users do like to see their heart rate on their watchface at all times.

So when I moved Arc Diem to Garmin, it seemed natural to include these features on the watchface, when I had not done so on the Pebble. Garmin makes them easy to include, and their users like and expect them to a greater degree than do Pebble users.

Garmins' app store has a lot of apps, but they're very focused on sports and fitness tracking; they don't have the variety of utility apps that was so impressive on the Pebble.

While we're on the subject of smartwatch philosophies, let's talk about Apple. Apple's philosophy is that they are Apple. They make very shiny devices, and their watches must be as shiny and impressive as their larger gadgets. This is why Apple watches put so much impressive capability into the watch itself, even to the extent that they get barely a day of battery life even without an always-on display. They know their customers are willing to put up with short battery life if it means Owning An Impressive Apple Device.

Pebble's philosophy is that the watch does not need to be an entire wrist-phone; it just needs to allow you to write the app that does That One Thing You Need. Apple takes the exact opposite tack, and does its best to be that wrist-phone and provide Everything. Garmin starts with the assumption that That One Thing You Need is probably the GPS and fitness data, makes that easy to get, and provides the capability of using the same data and the phone connection in other creative ways to get Some Other Fun Things. I wouldn't be surprised if Fitbit uses Garmin's philosophy as well, though they may settle somewhere between Garmin and Pebble thanks to their acquisition of the latter.

So it's safe to say that if Arc Diem gets ported to yet another smartwatch platform, its feature set may change again, just as the "same" video game changes a bit depending on which of its supported consoles it's running on. The different watches have different audiences, with different needs, and they provide different development tools in service to those needs.