Good posture isn't about holding yourself perfectly still. Healthy posture includes both position and movement. Posture uses the angle of your upper back together with activity from your back muscles to help you avoid staying slouched and inactive for long periods.
Attach the Puck over the upper-back muscle shown below, between your shoulder blade and spine. Make sure the Puck is oriented as shown.

Open Posture and select your connected Muscle Puck. Choose how long you'd like to be in poor posture before receiving a vibration reminder.
For example:
Posture also comes with three preset daily goals for how much of your wear time to spend in good posture: Downtime (25%), Desk Focus (50%) and Showtime (90%), for when posture matters most. You can also create your own goal at any time.
That's it. Muscle Puck will monitor your posture in the background. A minute of good posture combines:
You don't need to consciously flex your back every minute. Normal movement and periodically using your back muscles can provide the engagement Muscle Puck is looking for.
If you go for your selected reminder period without a good-posture minute, your Puck will vibrate. Use it as a cue to straighten up, move and re-engage your back muscles. Then continue with your day.

Want to see your muscles during exercise? Try the Power app →