[RPG] What does dice notation like “1d-4” or “1d-2” mean

According to Wikipedia, this is called zero bias notation^{(retrieved Aug 31, 2010)}. You simply replace the “d” with a “z” and the old highest die value with the new one. So your example of three eight-sided dice marked 0–7 would be written as 3z7.

The only reference the Wikipedia article provided for this was an RPGnet post. I've never seen any signs that the notation caught on anywhere, but I do like it as a system.

There sure is!

1. Pick a size of a pool of d20 dice. The bigger the pool, the stronger the results.
2. Next grab a d6, d10, a different colored d20, or even a coin.
3. Roll the die pool and roll the extra die.
4. If you got an even number on the die, pick the smallest roll from of the pool of die and use this as a result. Odd? You pick the largest die value from the pool.

With a pool of 4d20 I get the following results in Excel (using a total sampling of 10,000 rolls):

1   2   3   4   5   6   7   8   9   10
9%  8%  7%  6%  5%  4%  3%  3%  3%  2%

11  12  13  14  15  16  17  18  19  20
2%  3%  3%  3%  4%  5%  6%  6%  8%  9%

So roughly a 20% chance of critical success or critical fail, and a 4% combined chance of a 10 or 11.

Credit goes to sage for suggesting the even/odd roll instead of a coin.

And now some graphs, because everyone likes graphs, right?

Although technically this is bar-graph land, I included a line graph as well as I thought it made it easier to see in light of the number of bars that were being dealt with. I also increased the sampling to some 100,000 dice.