Q: I most likely skipped over the rule explaining this, but I have looked everywhere and I can't figure out what 18/00 means for ability scores. I get that 18 means you got the perfect roll, but what does the 00 mean?
A: A “perfect” 18/00 Strength score was mentioned in Design & Development’s Dice Weirdos article, and refers to early editions’ ability score generation. As stated in the 1st edition Player’s Handbook: “…strength is the major characteristic (or prime requisite) of fighters…. fighters with an 18 strength are entitled to roll percentile dice in order to generate a random number between 01 and 00 (100) to determine exceptional strength; exceptional strength increases hit probability and damage when attacking, and it also increases the weight a character is able to carry without penalty for encumbrance, as well as increasing the character’s ability to force open doors and similar portals.”
These percentile modifiers for Strength were dropped in the game’s 3rd edition. For more on earlier editions of the game, check out the D&D Alumni article: A Look Back at the Player's Handbooks.