Single width walls for perimeter calibration

There are wonderful calibration sets around. I've just made this one to learn Freecad and to make a fast printing thing to check just perimeter extrusion width (advanced perimeter and extruder tuning).

#How to
1. Slice the thing (be sure to set perimeters=1 in vertical shells) and open the gcode file.
2. Take note of perimeters extrusion width parameter. In my case it was 0.67, calculated autamatically by Slic3r for a 0.2 layer height with a 0.4mm nozzle.
3. Print.
4. Measure it. Don't i