Hi there Aerodyno,
I just checked, and the input box for changing the Cartesian grid size does not appear to be working. Looks like you've discovered a bug. I'll have an hotfix version (v0.12.1) of the Visualizer released tomorrow which will resolve this bug and a few others. Thanks for posting!
As for making sense of the data, the 0° mark is in line with the positive x-axis. This mark is also identifiable on the face of the device (LED and thin groove). The data azimuth increases in the counter clockwise direction as viewed from above (default camera orientation) in the visualizer. For more details, I'd recommend looking through the responses in this thread: http://community.scanse.io/t/data-plotting-formula/249
Let me know if you have any other questions.