When I used to wear a watch on a regular basis, the feature I used most was the stopwatch. I remember timing myself running around a track or around the block in high school and college. Eventually I stopped wearing a watch, but that’s about to change when the Apple Watch ships. I’ll be getting one as soon as it’s available, and I’m excited to also be bringing a version of Runtime to the watch.

Runtime for Apple Watch is a feature rich stopwatch fit for the age of the iPhone. It’s what you would expect a stopwatch to be in the age of the smart watch. Not only can you fully control a run from your wrist, you can see your current location, split times, stats, and an elevation profile all at a glance while you’re out on the trail – without ever touching your iPhone.

The Apple Watch version of Runtime builds on top of Runtime 2.0 which was released for iOS 8. That version included the Stopwatch Widget and advanced statistics support. Both of those features proved to be key stepping stones towards building a great watch app for Runtime.

Runtime’s Stopwatch Widget is a close cousin to Runtime for Apple Watch, but it’s amazing how much more capable WatchKit apps are than Today Extensions. For starters, WatchKit apps can open their iPhone app in the background, so you can start a new run from your watch without ever touching your iPhone. You can also navigate between pages of information on the watch, which is how you swipe between the Runtime stopwatch, current location, split times, and elevation profile.

Another key to building Runtime for Apple Watch is MMWormhole, a lightweight message passing library I worked on at Mutual Mobile. MMWormhole drives everything about Runtime for Apple Watch. It keeps all the statistics up to date and relays all of the start, pause, cancel, and save commands from the watch back to the iPhone.

When WatchKit was announced, I wrote about the limitations of the built in interface timer control. I ended up not using the control in the shipping version of Runtime. The irony though, is that I’m not using a label for the elapsed time either! My friend and designer Ryan Considine came up with the brilliant idea to include the elapsed time inside the start/pause/resume button, which is exactly what I’m doing. Fortunately, MMWormhole is capable of relaying the elapsed time every second to the watch, resulting in an accurate display of information as the title of the button. I’m really happy with how this design maximizes use of the space on the watch.

The elevation profile is really a killer feature on the watch. I had the idea for this while I was out hiking at Big Bend. I wanted to see how far up the ridge I was to get an idea of how much further I had to go. Elevation is key to cyclists as well, many of whom also use Runtime. An elevation profile that shows the elevation of a completed run was already part of Runtime, but there wasn’t yet a concept of the elevation on your current run or hike. I added that to the iPhone soon after, and it’s a huge addition to the watch as well.

The challenge with building the elevation profile on the watch is that WatchKit doesn’t include support for custom drawing like you would do to render the graph of an elevation profile. To work around this limitation, I am rendering a version of the elevation profile graph as an image on the iPhone, and transferring the image over when you view the Elevation page on the watch. This trick is a great way to include rich and detailed information on the watch that you can access quickly without pulling out your phone.

Another new concept to both the iPhone and Apple Watch versions of Runtime are split times. Runtime’s splits are your mile or kilometer times. A split time is recorded automatically every mile or kilometer without pushing a button. Many distance runners use Runtime, and having an automated way to track their mile times is a great way to measure training progress and overall endurance. I think this’ll prove to be a popular feature on both apps.

Glances are a great new interface paradigm on Apple Watch. Runtime’s Glance is very similar to the default state of the Stopwatch Widget, which shows your total step count for the day. I really like keeping track of my daily step count, which is why this features so prominently on Runtime’s Glance. Runtime’s Stopwatch Widget remains one of the few Today Extensions that I use on a regular basis, and I expect I’ll frequently use the Runtime Glance as well.

While a run is in progress the Runtime Glance also shows all the relevant stats for your current run, including your location, time, pace, and distance. If a run isn’t in progress, you can always tap on the glance to start a new one!

I’m really excited to ship this update to Runtime with support for Apple Watch. The update also includes a few bug fixes, as well as the new accompanying features on the iPhone’s stopwatch screen. I was initially a bit skeptical of WatchKit when it was announced in November, and worried about building a watch app that required the presence of an iPhone. But now that the app is finished, I’m actually very happy with what I was able to do with it and really looking forward to getting my watch so that I can use this on all my runs going forward.