*PlanetsCentral* classifies games according to their difficulty using various criteria:

- ship list difficulty (expensive ship lists are harder to play than cheap ones)
- universe mineral and native difficulty (rare universes are harder to play than rich ones)
- production difficulty (higher production rates are easier than low ones)
- add-ons can increase and decrease the game's difficulty further

Each of these ratings yields a scale factor, conveniently expressed as a percentage. Multiplied, these give the game's difficulty. A standard Tim-list game has a difficulty of about 1.0 = 100%. A standard PList game has a difficulty of about 1.35 = 135%.

### Ship List Difficulty

The ship list difficulty judges the cost of ships in this game. Therefore, it computes the average cost of a ship.

- find the best engine (=first that goes warp 9 at 120% fuel usage or less)
- find the best beam (=maximum combined kill+explosive value)
- find the best torpedo (=same)
- build one ship of every type, equipping it with the above engines and weapons. Add up the Tritanium, Duranium, Molybdenum and money cost.
- compute the average cost.

Ship_list_difficulty = (Average_ship_cost / 2000)^0.33

The standard ship list has an average cost of approximately 2000, PList has about 5000, PList-heavy has about 10000. Therefore, a ship list has difficulty 1.0 if it is similar to the standard ship list.

### Universe Mineral Difficulty

The mineral difficulty judges the mineral richness of the universe, i.e. your ability to obtain minerals for building ships.

Mineral_difficulty = (1800 / (Average_surface[T,D,M] + Average_ground[T,D,M]))^0.33 Average_ground[x] = (Adjusted_freq[x] * Average_usual[x]) + ((1 - Adjusted_freq[x]) * Average_alternate[x]) Adjusted_freq[x] = 1 - (1 - PlanetCoreUsualFrequency[x]/100)*0.25

The `Average_surface[x]`, `Average_usual[x]`, and `Average_alternate[x]`
are the average amount of minerals of type *x* produced by the
`PlanetSurfaceRanges`, `PlanetCoreRangesUsual`, and `PlanetCoreRangesAlternate` options.

The `PlanetCoreUsualFrequency` is adjusted to give more weight to the "usual" values,
to compensate the additional logistics required to move minerals from an "alternate" planet
to a "usual" one. Also, a planet with 10000 kt minerals isn't worth 10× as much as a planet
with 1000 kt, because you'll probably not spend it all.

With this formula, a universe has difficulty 1.0 if its planets provide 1800 kt minerals (=600 kt Tritanium, Duranium, Molybdenum) on average.

### Universe Native Difficulty

The native difficulty judges the native population of the universe, i.e. your ability to obtain taxes.

Native_difficulty = (25000 / Average_natives)^0.33 Average_natives = NativesOnPlanetFrequency * Average_native_clans / 100

`Average_native_clans` is the average number of natives on a planet that has natives,
determined from the `NativeClansRange` or `NativeRange` options.

A universe has difficulty 1.0 if its planets have 25000 native clans (=2.5 million natives) on average.

### Production Difficulty

The production difficulty judges the production rate host settings, i.e. your ability to make use of the material provided on the planets.

Production_difficulty = 100.0 / Average_VPI Average_VPI = -8.0 + 50*(1 + (Average_ProductionRate-100)/100)^0.66 + 50*Sqrt(Average_MiningRate/100) + Sqrt((Average_NativeTaxRate + ColonistTaxRate)/2 * (1 + Average_HissEffectRate/5))*0.8

This is the same formula as used to rate the game difficulty for the VPI, the VGA Planets Player Index.

The `Average_Xxx` values are the average value of the respective host configuration
option. The `Average_HissEffectRate` is considered as 0 for players who do not have Hisss.

A game with normal settings has a difficulty of about 1.0 here.