How do skills combine?

[Supamand]

I think in the RO case, the value you see before you colonize the planet is the maximum production rate of RO. After you colonize, you see your current RO production rate, which is zero if you haven't learned the first rank of Advanced Mineral Collection. I believe the percentage quoted in the skill listing, at least for AMC, are percentages of the planet's maximum production rate (which you can't see anymore). The first rank of AMC both "activates" the ability, and increases your collection rate from 0 to 3% of the planet's max.

That is correct! As a trader you can see that distinction much clearer. For example I found a Jovian planet that said it could produce 400 RO. After I dropped and outpost, I was only getting 40 RO, because of traders 10% bonus.

[Royce]

That is correct! As a trader you can see that distinction much clearer. For example I found a Jovian planet that said it could produce 400 RO. After I dropped and outpost, I was only getting 40 RO, because of traders 10% bonus.

That's exactly what I was referring to in my first post. Percentages really don't ever seem to be a percentage of the actual current value. Ore production percentage increases are a percent of total possible production. Trade value percent increases and decreases are not a percentage of the value you currently get, but are a percentage of the total base trade value (so a 10% percent increase is actually a 20% increase from your base share). I see no reason to assume combat modifiers are any more transparent. It's probably nowhere near as simple as the possible equations you've proposed above.