Smart Ruler can display a ruler or protractor at the edge of the display. This enables on the fly measurements with the smartphone. It belongs to the Privacy Friendly Apps group developed by the research group SECUSO at Technische Universität Darmstadt. More information can be found an secuso.org/pfa/ What makes Privacy Friendly Ruler different from other similar apps? 1. No permissions Privacy Friendly Ruler does not require any permissions. 2. No advertisement Many other free apps in the Google Play Store dazzle annoying advertising and also shortens battery life.