To my understanding, it calculates at what percentage you are of the highest value in the category.
Example:
On East Continent, the highest prestige a character has is 100.
Your character has prestige = 10
Your value in ShowFame would be 10 (%) for prestige.
If you are the one with 100 prestige, the ShowFame will tell you 100 (%) for prestige.
And it does that for all kinds of definitions. (Skills, reputation, lordship,..)
