Hi Fil, just a quick note on this:

> I need a ruler in order to control some distances..

Currently you can draw a line to find the distance between 2 points - while you are drawing the line look at the distance readout in the bottom toolbar, here:




Also once you have drawn a line you can select it and the length of it is displayed here:




There's also a plugin command that you can install to get a "Distance" command as well:
http://kyticka.webzdarma.cz/3d/moi/#MeasureDistance

- Michael