The Edge Screen on Galaxy S7 is getting more functional and easier to use than the Note Edge and S6 Edge. The Quick Tools lets you use the edge screen on Galaxy S7 as ruler and can be enabled and used by doing as follows:
1. Open the Settings application on your S7 Edge
2. Go to the Edge Screen settings
3. Tap the Edge Panels settings and make sure it is toggled on
4. Now under the Edge Panels tab, swipe to find the Quick Tools panel (Look for the Compass).
5. Make sure to mark the Quick Tools, so it will be shown in your edge screen
6. Now go to the home screen and swipe from the edge of the screen to bring up the edge panels
7. Swipe to the Quick Tools and then touch the Ruler icon from this panel (Compass and Flashlight are the other opions)
8. Now your Edge Screen will function as a Ruler on your Galaxy S7 Edge