• Each scanner component has a given rating in light-years (ly), within which radius it can detect uncloaked ships in deep space. Some scanners (known as "planet-penetrating scanners", or "penetrating scanners"/"penscans" for short) additionally have a second, lower rating, within which radius they can detect uncloaked ships in orbit of a planet, uncloaked starbases, and the statistics (owner, population, mineral concentrations, habitability values) of planets themselves. The population of Alternate Reality races' planets will always be reported as 0, no matter what it actually is. Claim Adjuster races, when viewing scan reports of a planet inhabited by a race they have set to "friend", will see the owner's habitability bars instead of their own.
  
• In addition to scanner components mounted on ships, there are a few other things that have detection capabilities:
  - Planetary scanners: inhabited planets can construct a "Planetary Scanner" from the production queue. This will use the rating(s) of the best planetary scanner component you have the tech for (it's automatically upgraded when you discover a new one).
  - AR planetary scanners: planets controlled by an Alternate Reality race cannot construct planetary scanners, but instead receive an organic scanner dependent on the population of the world. All worlds receive an ordinary scanner with a rating of (SQRT(population/10)), and worlds with an Ultra Station or Death Star starbase receive a planet-penetrating scanner with half that rating. There doesn't appear to be a cap on this formula, but very strange things happen when you put over 1 billion pop on a world.
  - SD "minefield scanning": Space Demolition races' minefields act as ordinary scanners; ships in deep space within a Space Demolition minefield will be detected by the minefield's owner as though they had been scanned.
  - PP "packet scanning": Packet Physics races' mineral packets act as scanners; packets have an ordinary and planet-penetrating rating equal to the square of the warp speed at which they are flung (e.g. a packet flung at Warp 12 will detect ships and planets within 144 ly). Packet Physics races can also detect all mineral packets and deep-space scrap in the universe.
  - IT "gate-scanning": Interstellar Traveller races' stargates act as special scanners, with a rating equal to their distance rating as a stargate. These scanners will detect planets with starbases that have stargates, and

• I've seen people arguing both that NAS is better for detecting minefields/wormholes and that penetrating scanners are better for detecting them. Given that penetrating scan range is about half of ordinary scan range, that NAS doubles ordinary scan range, and that minefields/wormholes are 75% cloaked vs. ordinary scans but uncloaked to penscans, the ultimate answer is that by and large they're about even once decent penetrating scanners appear at Elec 10. If you want a full breakdown:
  - Before penetrating scanners are available, NAS is going to have twice the detection range of non-NAS. Obviously.
  - The Ferret Scanner has a short penetrating range of 50 ly, while NAS races will have 75 ly (Possum) or 112 ly (Gazelle).
  - The Dolphin Scanner has a penetrating range of 100 ly, while NAS races will have 112 ly (Gazelle) or 137 ly (Cheetah).
  - The Elephant Scanner has a penetrating range of 200 ly, while NAS races will have 167 ly (Eagle Eye) or eventually 250 ly (Peerless).
  - Complicating this is that planetary scanners stop improving at Elec 8 for NAS races, while they continue to improve for penscan races. This means that at Elec 10, along with the Dolphin Scanner a non-NAS race is going to have the Snooper 320X planetary scanner and as such 160 ly of minefield detection from their planets. And at maxed Electronics against the NAS Peerless's 250 ly the penscan race also has the Snooper 620X and its 310 ly penscan range.
  
• Keep in mind, when putting scanners on Frigate and Galleon designs, that a second scanner adds only 19% to the first scanner's range. It's often worth it anyway, but not always.

• I made a spreadsheet a few days ago comparing cloak units required to get a given cloaking % and the increase in scanner range required to beat that cloaking %. XAPBob has been kind enough to host it here.
  
• The graph at the top (and another graph to the right of it) plot for every %cloak the cloak units/kT required to achieve that value and the increase in scanner range (or equivalently, scanner number in a picket line) needed to breach that %cloak. For instance, you need 420 cloak units/kT to achieve 80% cloaking, and you need 5x the scanner range to detect it, so there's a point at (420,5). The graphs only differ in that the one on the left uses a logarithmic scale.
  
• The graphs further down plot the total and marginal "efficiency" of various cloaking percentages. The total efficiency is defined as (increase in scanner power required, % of range vs. uncloaked)/(cloak units/kT required). The marginal efficiency is defined as (increase in scanner power required, % of range vs. uncloaked, compared to 1% less cloaking)/(increase in cloak units/kT required, compared to 1% less cloaking).
  
• Follow the blue lines marked "Normal" for now. I'll get to the red lines later.
  
• What can be seen from the efficiency graphs is that there are two rather different "sorts" of cloaking. There's "partial" cloaking, in which you cloak a fleet up to the 50% or 75% breakpoints for a relatively small expenditure, and there's "full" cloaking, in which you use a larger investment to go for 98% or as close to it as you can get. "Full" cloaking is far more efficient in terms of the amount of scanning required to defend equivalently against it, to the point where it becomes infeasible for much of the game for opponents to breach 98% cloaking over any significant distance (a Galleon full of Eagle Eye Scanners only achieves 11 ly range against a 98% cloak). Some awareness o

That is some good stuff. Would you show the how SD field scans work?

Are you sure? I am not arguing, I just seem to remember differently. Something like range instead of probability? Maybe what I remember is having this discussion before.