This fitbit app can be used as a pacemaker. Set your target distance and the time in which you would like to run that distance. E.g. 10 km in 40 minutes. Every 10 seconds the app will calculate your speed and extrapolate how long it will take you to run your target distance. It indicates whether you should speed up or slow down. You can switch between different views using the left button and switch the units from m/s to km/h and min/km by using the upper right button. Your run will be tracked as exercise and you can access it in your fitbit dashboard. As the right buttons are needed the app is only available for Ionic and Versa, not for Versa light or Versa2. You can check out the source code on my git https://github.com/horseshoenail/pacemaker.