@sepdek's

In order to be a measure (distance) d must:   In order to be a metric (distance) d has to be a measure and:   …and here is the cheat sheet:  

A newly developed remote monitoring app for Android devices has been published on the Google Play store. The application is a miniaturised version, which provides just a few remote measurements served by a data server. The application is heavily based upon the work of Maria Pappou and Christos Zaptses, which have originally developed an arduino-android […]