Ruler is a free Android app developed by SOFTDX that allows users to measure the length of small objects using their smartphones. The app is easy to use and provides accurate measurement results when calibrated to the actual size of the ruler.

The app is equipped with various features, including a measurement line, two measurement lines, double-click initialization for measuring, and Cm or inch settings. It also allows users to choose between left and right grid layout to provide more convenience during use.

To use the app, simply calibrate the ruler to the actual size of your smartphone screen, place the small object to be measured on a flat surface, and touch the screen to display the measurement line. The value of the measurement will be displayed on the screen.

Overall, Ruler is a useful app for anyone who needs to measure small objects and wants to avoid the hassle of carrying a physical ruler. Its accuracy and ease of use make it a must-have utility app for Android users.