D10s, Add-Ons, and the Missing TN 11

[LandonSuffered]

Since this is a forum for game designers I thought I’d post this short question here. Background first:

I’ve had some complaints in the past with D10 games that have open-ended rolls (roll a “10,” roll again, and add the result). The main complaint is that TN 11 is the same as TN 10 (if you roll a 10 you always will add at least a “1” with your second roll).  This includes all numbers directly after a 10…so 11, 21, 31, etc. In games where TNs get pushed because of extra difficulty for extended maneuvers, there is no risk involved in pushing up the TN 1 more when you’ve reached one of these magical break-points.

The way I’ve fixed this in the past is when you roll a “0” on the D10, your next roll adds to 9, not 10.  This way the 2nd roll will add 1-9 giving a value of 10-18, with a 2nd 0 meaning "roll again and add to 18 (double 9)."  For most rolls the addition doesn’t get too bad, as people aren’t rolling a bunch of double and triple 0s.

Here’s the short question:  is there already a game out there that uses this mechanic?  I haven’t seen it before, and I'd be curious to read some reviews that talk about probabilities using a base-9 die system. 

Thank you!

[rafial]

is there already a game out there that uses this mechanic?

I've not see it with d10s, but I have seen it done with d6s.  The original mechanics for Prime Directive used an exploding d6 roll, where the reroll was added to 5, for just the reason you outlined above.

-wilhelm

[Adam Dray]

I've seen it with d10's. A Google search came up with some results that reflect this. I haven't search the forum for any yet.

[Valamir]

You can have similar work arounds for die pool systems where each die that is equal or under a given TN is a "success".

With a TN of 11 then you simply treat the TN as 10 and then have results of 1 count as 2 successes.  With a TN of 13 results 1-3 count as 2 successes.

To get away from the automatic success of a TN of 10 (on 1d10), you can make this wrap around feature start earlier...say anything above TN 8 wraps around so that 9s and 10s are always failures.  With a TN of 13 then 1-5 would count as 2 successes, 6-8 as 1 success, and 9-0 as zero successes.

Which happens to be the system Robots & Rapiers uses.