Open d100

This is a way of rolling a 100 sided dice to produce a random number. The computer actually uses a pseudo-random number generator (PRN), but the effect is the same.

A 100 sided dice produces a number between 1 and 100. The open part of the roll adds the following rules:

• If the roll is greater than 95, roll again and add the result.
• If the roll is less than 5, roll again and subtract the result.

These rules are applied recursively, so very high and very low rolls are possible (but unlikely).

There is about a 1 in 20 chance of rolling unusually high and an equal chance of rolling unusually low. A second roll in either direction occurs about 1 roll in 400, and a third about 1 in 8000.