The Great Apple
Big Cheese
Not all Europeans use commas instead of decimal points! This map is quite interesting: http://en.wikipedia.org/wiki/File:DecimalSeparator.svg. The one that really annoys me is when people from the US use mm/dd/yy instead of dd/mm/yy in dates. It's especially bad if the day is below the 12th, as it's never clear which convention is being used!
Anyway... topic. I think everything is additive. The one that often catches people out is India's +100% unhappiness from number of cities. As this is additive, you cannot reduce unhappiness from number of cities to 0 using planned economy & FP (each -50%). Instead you just get what normal Civ's get. I tend to think that additive is more intuitive when it's a +ve modifier, and less intuitive when it's a -ve modifier... though given they often mix that wouldn't really work!
Anyway... topic. I think everything is additive. The one that often catches people out is India's +100% unhappiness from number of cities. As this is additive, you cannot reduce unhappiness from number of cities to 0 using planned economy & FP (each -50%). Instead you just get what normal Civ's get. I tend to think that additive is more intuitive when it's a +ve modifier, and less intuitive when it's a -ve modifier... though given they often mix that wouldn't really work!