NEAL'S RULER FOR WINDOWS PHONE
screen3

This is an app that runs on any Windows 7 Phone and higher that has two edges of a ruler. One edge has metric marks (centimeters) and the other side has standard marks (inches). It also has a button that allows the edges to be switched so the metric side can change places with the standard side. It can be installed from the Microsoft Store app page.

Screen Shots From Neal's Ruler for Windows Phone

screen1 
screen2 
screen3 
screen4