Hi Pal, you shd put the dial at 'M' for a day, 24hrs (without any equipment in it).
The ideal reading is around 40-45%. Any reading above 45%, turn the dial clockwise (towards the red zone) slightly, than monitor, and adjust accordingly. If reading is below 40%, do the opposite.
After the huminity is stable, than put your equipment in and monitor for a few days. Adjust accordingly.
Hope this help.