Using a 42mm Apple Watch Sport paired to my iPhone 6. For the past 5 days I've used the Workout App and the Outdoor Walk exercise to monitor a walk of 2-4 miles each day. It shows that I walk about a mile in 20-23 minutes and the average heart rate and tracked heart rate look reasonable. But for a walk that takes around 20 minutes each way, instead of 40 minutes of exercise it credits me with 3-7 minutes in the Activity app on the Watch and iPhone. My Exercise Ring is lagging! The documentation talks about 'brisk' activity whatever that is. I'm 67 and am walking my normal pace which includes waiting for road crossing signals and pausing briefly to say hi to neighbors. Anyway for me to change the calibration for 'brisk'? I do carry the iPhone along in my pocket so it can get the most accurate distance information.