# The Game System
“Skill rolls” may be called for during dramatic situations in the game. Walking down a well-lit hallway is not a dramatic situation, whereas running down a rubble-strewn corridor while being chased by monsters most definitely is!
When attempting a skill roll, you should agree a goal with the Keeper. If your skill roll is successful, you achieve your goal. Additionally, when you successfully roll a given skill, put a check mark in the box next to it on your investigator sheet. You can only get one check per skill at a time. At the end of the scenario, that skill could increase due to experience—see Rewards of Success, for further information.
On occasion, you may need to roll a test that is not covered by the skills on your sheet. If so, look at your investigator’s characteristics and determine which one of them is best to use and treat it like a skill.
# Roleplaying Dice
Call of Cthulhu uses a set of roleplaying dice. These “polyhedral” dice include: percentage dice (D100), a four-sided die (D4), a six-sided die (D6), an eight-sided die (D8), and a twenty-sided die (D20). Dice sets can be purchased at most hobby game stores and online, and there are also online dice rollers too.
The letter “D” stands for “dice.” The number after the D is the range of numbers available: 1D8 generates random numbers 1 through 8, for instance, while 1D100 generates the numbers 1–100.
In a written adventure, the text might say a monster delivers 1D8 damage, meaning that a 8-sided die is rolled once to determine how much damage is actually caused.
# Reading D100 (Percentage Dice)
Percentage dice usually consist of two 10-sided dice, which are rolled at the same time. One die (units) is numbered 1 to 0, the other (tens) being numbered 10 to 00. Both dice are rolled and should be read together (e.g. “30” on the tens die and “05” on the units die is read as 35%). A roll of “00” (tens die) combined with a “0” (units die) indicates a result of 100%. A roll of “00” on the tens die combined with any other roll on the units die indicates a roll of under 10%; for example, a roll of 00 on the tens die and 3 on the units die is read as 3%.
# Dice Roll Variations
Sometimes a dice notation is preceded by a number other than “1.” This means that more than one die is rolled and that their results should be added together. For instance, 2D6 means that two 6-sided dice are rolled and totaled (or roll a D6 twice and add the scores together).
You might also see 1D6+1, for instance. This means that the number following the plus sign should be added to the result of the D6 roll. For 1D6+1, the result must be 2, 3, 4, 5, 6, or 7. If a monster claws for 1D6+1+2D4 damage, find the power of the actual attack by rolling the two requested dice, totaling the results, and adding 1 (rolling 1D6 and 2D4, then adding 1 to the total rolled).