Ruler by O.D. is a free measuring tool available on Android. It is a simple and accurate application that allows users to measure objects by touching their screens. The app's interface is straightforward and easy to use, making it an ideal tool for both personal and professional use.

One of the main features of Ruler is that it allows users to fine-tune measurements in 0.1mm increments using buttons on the screen. The app measures only in millimeters, but it is accurate and reliable. Another advantage of Ruler is that it is only as big as the user's screen, making it easy to use and carry around.

Overall, Ruler is a useful and reliable measuring tool for Android users. Its simplicity and accuracy make it a great addition to any toolbox. However, it lacks some advanced features, such as the ability to measure in other units or save measurements for later use.