Feanor wrote:
The system had a difficulty X roll a dice pool of N d10 and count all the dice greater or equal to the difficulty X BUT subtract 1 for every 1 rolled.
Also if the skill was equal or greater then the difficulty the result was supposed to be an automatic success.
Combining the results and the thumb rules I converted the Vampire dice system to a strait d% with skill=difficulty=>100 EML and -10 EML for every skill level less.
Rather than sum up the -1's to to get results totaling less than 0 to determine "dramatic failures" I made it into the Harninc max EML is 95 and failures ening in 5 or 0 resulting CF (dramatic failure).
The result was immediately familiar to Harnmaster players, was a lot faster and easier than the Vampire system and produced similar results.
In the Vampire system rolling Damage or Effect though was often done separately from the initial roll: first roll dex+melee of 7d10 vs difficulty X and add it up >0 to determine if a success and then if successful roll str+melee of 8d10 vs difficulty of 6 to get damage. Instead the Success was a HarnMaster like d% roll and then the damage was rolled as in Vampire.
Although rolling Nd10 and adding together number of dice greater than X can be a bit bulky to determine Effect/Damage it does produce some beautiful probability distributions. With difficulty 6 (the default) it produces a binary distribution bell curve like flipping a number of coins and counting heads (not unlike rolling 3d6 or whatever). But altering the difficulty higher or lower than the 50/50 coin flipping situation shifts the bellcurve in ways rolling dice and adding would have difficulty reproducing.
Attachment:
Difficulty vs Effect example.jpg
In some ways what Harn Master achieves thru multiple success levels and xd6+weapon impact this other system accomplishes thru altering the bell curve. Imagine overlapping and combining the 1d6,2d6,3d6&4d6 impact dice as a rough bellcurve weighted to the low end - shaped similar to the difficulty 9 damage curve above for 10 dice (.1 near 0, peaks at 2, slopes slowly to 0 at 6).
(If you haven't guessed from the above our Harn Group is currently playing a round of 1992 AD Vampire.)
Anyway, even if you can't calculate it directly repetitive testing and a sufficient sample size can often produce an accurate model/estimation. We were actually using similar techniques a lot in my advanced engineering math courses in college - though obviously if you build a bad model with wrong assumptions you get results that have no bearing on reality (for example the numerous global warming model predictions).