Play any game of Civ4.
Before you have libraries or any other "precentage" boost to commerce, and you have an odd total current GDP (sum of all commerce values in the top-left of your screen), change the culture sliders to the following:
100% research, 0% cash, 0% spies, 0% culture
100% cash, 0% research, 0% spies, 0% culture
50% research, 50% cash, 0% speis, 0% culture
If, for example, you had 11 current GDP at 100% research, you'd have 11 current GDP at 100% cash. However, you'd have 10 current GDP at 50% research and 50% cash.
This is caused by the fact that the game "rounds" your total cash/research after adding up each city's contribution into the whole pot.
I am not absolutely certain that this is a display bug or not. But if it is a real bug, then you can get a rather significant boost to your total commerce by doing "binary" research, where you move the slider from 100% research to 0% research, having your treasury flux between negative and positive growth.
Before you have libraries or any other "precentage" boost to commerce, and you have an odd total current GDP (sum of all commerce values in the top-left of your screen), change the culture sliders to the following:
100% research, 0% cash, 0% spies, 0% culture
100% cash, 0% research, 0% spies, 0% culture
50% research, 50% cash, 0% speis, 0% culture
If, for example, you had 11 current GDP at 100% research, you'd have 11 current GDP at 100% cash. However, you'd have 10 current GDP at 50% research and 50% cash.
This is caused by the fact that the game "rounds" your total cash/research after adding up each city's contribution into the whole pot.
I am not absolutely certain that this is a display bug or not. But if it is a real bug, then you can get a rather significant boost to your total commerce by doing "binary" research, where you move the slider from 100% research to 0% research, having your treasury flux between negative and positive growth.