There are a ton of really great videos, tutorials and technical information available on scanning in Eve. This isn't one of them. This is the famous Idiot's Guide, which is my sarcastic way of saying, this is my guide - there might be others like it - but this one is mine.
Like my other Idiot's Guide posts, which are all extremely helpful, this one is solely based on my own personal experience and has nothing to do with specs, maths, or other types of complex thought. No diagrams or charts. Just how it is done.
I use d-scan every single moment I am in space, in fact my scanner window is always open and I use it all the time. In fact it often tells me to stop cause it needs to re-calibrate. Poor thing.
So how does the d-scanner work? I honestly have no friggin' clue. What I do know, which is all that really matters, is how I use it to find you and kill you. If you'd like to know how to also do that, then read on.
A Question of Degrees
You might remember from High School that a circle is 360 degrees around. Imagine a big circle surrounding your ship with the center right smack dab in the middle. You can actually see the center of your ship when you right-click on it or engage comms. The directional scanner works by shooting invisible magic rays out from the center of your ship into space, instantly telling you what is out there. It can do this by degrees and distance.
If you want to know what is around you in a complete circle then you scan at 360. Now, it is important to remember a few key facts here. Distance is an issue, your scan is only good out to a certain distance, about 14AU ish. (Funny, no one seems to know the exact number) As you scroll the degree control down (It is the slider at the top of the directional scan window you Idiot!) the degrees go down and the scan narrows. All the way down to 5 degrees. This is when magic happens and the directional scanner actually becomes directional.
So what direction though? How do I know where I am pointing, there ain't no directions in space?!? Calm down, this ain't hard. Imagine a straight line from your eyes, thru the center of your ship and out into space? That line is the line of scan. At 30 degrees it is wide, at 15 pretty narrow, at 5 it is almost a laser. I mention 30,15 and 5 because, other than 360, those are the only ones I use.
With me so far? I'll wait while you review.
Finding a Target
You've jumped into a system to hunt. Your d-scan should be set at 360 already, I do it when I jump, it has become habit. The moment I de-cloak I scan the system. My d-scan is synced with my overview (You'll see the checkbox on the d-scan window, use this!) so the returns are manageable and not 400 pages long. It does no good to scan everything in the system, you want ships! So scan for ships. My overview is sorted by distance, near to far, so a quick glance at the overview can tell me what would NOT have been included in that 360 scan. Since no ships appeared, it looks like Planet V is out of scan range!
And lo and behold Planet V has belts! At this point, depending on your aweseomness, you either warp to the planet or a sfae spot you already have set up for doing this. Let's assume the Planet. Warp there, while in warp narrow the scan down to 15 degree. The moment you land start swinging your ship around to the belts, the icons should be in space. Align your eye/ship center/target line and hit scan. Practice this and you will get very very fast at it. Belt V-4 has a Rupture in it! Or does it?
Belt V-4 is also in line with a Station, their icons are almost on top of each other. So how to tell? Scroll that bad boy down to 5 degrees. Now this can be tricky, you need the icon for your ship center to show, its a white box that shows the center of your ship. I have a hot key for it, I suggest you make one. Align the white box over the target icon and hit scan. Damn, the Rupture isn't in the belt at all (because no one really rats anymore) and he's hugging the station. Bummer :(
At this moment I suggest bringing the scanner back to 360 and making sure someone isn't about to land on you! You should have been aligned and burning towards something that entire time btw, do I have to tell you everything?
Where to scan?
And that brings up our next point. Working the scanner takes your eyes away from scanning for enemies coming to kill you, so keep your eyes on local, align, burn, the usual stuff. But it also pays to be prepared. We all end up scanning at planets, moons, belts, wherever we have to be, but it is a great idea to have some safe spots to scan from.
Any safe spot will do, but there are distance limitations to consider. To counter this I usually set up a scan spot off the Sun, usually about .2AU, in the center of the system. Where is the center? Why it happens to be the Sun, every singe time!
In some systems this spot will allow you to scan everything in space, in some it won't. It also happens to be the first place people will look for you when they start probing, but that's another post.
Make safe spots. Make a lot of them.
This is by no means a full guide to the d-scan. I suggest reading this one if you want more detailed information. But I've never read it and I just gave you the sum total of knowledge you need to scan down an enemy ship and kill it. If you happen to be a carebear person, just leave the d-scan alone, it won't help you. In fact I don't think it even works, so pay no attention to it.
PS: As with most things, you remember stuff after you're done, here are a few stoopid things I remembered:
• When jumping into a system you can scan before you de-cloak. This is one of the few advantages you have over people already there. Of course, if they have a blob at the gate you won't need to scan.
• This is the subject of another Idiot's Guide, but the overview is extremely important. I said above that you only need to scan for ships, which is true at first when you are hunting. But you should also have other overviews that show other things, like POS structures for example. The guy you are hunting may be hiding in one.
• I also mentioned I use 30 degree. I lied. I honestly can't remember ever using it, I always use 360, 15 and 5. This article isn't only for Idiot's, it was written by one.