How do you work this thing...(Radio Room Radar)?

I just find myself sitting and staring at the screen at a constant green line twitching around. The radioman seems to have no problem being able to detect ships and give me there exact bearing with no problem and he is just a seaman. I am the Captain of this vessel and I feel ashamed of myself for allowing a seaman to know more about the equipment than I do. Can a fellow skipper give me some guidance please? The bloody manual for this sim is worthless and is currently being used as a coffee mat.

Note to self: Must kick that seaman off the U-boat when we return to port, he is making me out to look like a worthless fool!!