Whenever an element of chance comes into play, you or the gamemaster roll a number between 1 and 100 using two ten-sided dice (d10). One (to be determined before the roll) represents the “tens” of the result, the other then “ones”. Rolling two zeroes means the result is 100. We call this a d100 roll.

Rolls can have modifiers added to them. Such rolls are described as e.g. d100+27, meaning “roll a d100 and add 27 to the result”. Similarly, d100-53 means you have to subtract 53 from your dice roll.

Rolls can be open-ended.

d100> describes a high open-ended roll. This roll yields values from one to, theoretically, infinity. You roll d100, and if the roll value is 96 or above, you roll again adding the second roll’s value to the first. Repeat the procedure until you roll below 96.

d100< describes a low open-ended roll. If you roll five or less, the value is discarded, but you roll again. The following rolls are treated like d100>, except their sum is inverted, yielding a negative number.

d100<> describes a fully open-ended roll. It’s treated as a high open-ended roll if your first roll yields 96 or higher, and as a low open-ended roll if it yields 5 or less.

Any of the open-ended rolls can have modifiers. The canonical form of describing such rolls is to first list the type of open-endedness, then the modifier, e.g. d100>+10, d100<+75 or d100<>-20^{1}.

Limited range rolls are also used, but very rarely. They’re written as e.g. d37, meaning a roll with values from 1 to 37. Limited range rolls can also have modifiers, e.g. d37+23. You have two choices for handling these rolls.

You can either roll d100, and re-roll every value larger than the range allows until you reach a result that’s within the range.

Alternatively, you can divide the roll value by one hundred, and multiply the result with the range limit (37 in the example above). For a d37 roll with a roll value of e.g. 63, that’d mean calculating ((63 / 100) * 37) = 23.31. Modifiers are applied to this result, not the roll.

This lists the steps you need to perform in order, i.e. first roll d100, then (possibly) handle open-endedness, lastly apply the modifier. [↩]