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Some notes on skill system design, etc.

Steve Marsh's Skill System

Ever since I came up with a d20 system for D&D in the 1970s, I've been playing with alternate skill systems.  The following is one that I have that works well with Chaosium's Basic Role Playing System or Stormbringer.

This system is expressed in percentile terms. It translates easily into 3d6 terms and can be used in a 3d6 system (3d6 systems are generally superior to d20 systems, in my opinion).

BASIC SYSTEM (and yes, lots of examples follow)

Most tasks are determined by a roll of (skill + %tile roll) - (y*10%). y is determined by the degree of randomness/difficulty in the task. All skills are expressed as a number level as skill n%, where skill is the name of the skill and n% is the skill level. For each 5%tiles obtained above 0% one point of effect is done (rounding up {e.g. 1% is rounded up to 5% for determining effect).

For example, a character might have jogging at skill level 60% or jogging 60%. Jogging on a track is a 0 level, nonrandomized, task. The result of someone jogging on a track is determined without the randomizer (skill + 0%) - 0%. A jogging skill of 60% would mean that each round of jogging the character could do 60 points of jogging for 12 points of effect. <(60% + 0%) - 0%>/5 = 12. (with %tiles, divide the % by 5 to get the number of points. I.e. a skill of 60% would do 12 points a round in an unapposed situation).

Cross country jogging on a path is a 10% level task (i.e. y = 10%). The skill of 60 would do (60 + d10%) - 10% per round. In addition, tools can increase the result done. Magical boots or bionic shoes could add to skill, results or could alter the level of the task.

Non-magic tools add to the dice roll. Good shoes might add +2 to the results of jogging. Often tools have conditional impact. That is, a tool's addition comes only if a positive result is first made. This is most common in combat.


This system works well with combat. Treat combat as usually being a 100% level task. A skill of 60 would do (60 + d100%) - 100 points per round and would have a 60% chance to hit. With a normal 1d8 tool (such as a sword) at 60% skill one would do <(60% +d100%) - 100%>/10 per round at skill level 60%. Every positive roll would add 1d8 (for the conditional tool) to the result.

Parry skill can be added to combat by having the parry skill added to the minus side of the equation.

Thus 60% skill to hit vs 40% parry becomes (60% + d100%) - (100% + f(40%)[roll d100, if at 40 or less, the roll equals the number -- so a roll of 40 = 40 in defense, a roll of 05 = 5 in defense, a roll of 41 to 100 = zero impact) or d100% - 80% -- a 20% chance to hit (if the parry was perfect).


Some problems regenerate, some have initial difficulties. Many tasks can have help from tools. Let me give some examples.

Piloting a ship

Wavestalker has an enchantment worth +15% on a superior ship worth 10% and a skill of 30%. Leaving the harbor in his ship is a 3 point a round task.

That means, that to successfully leave the harbor Starstrider must earn 3 points each round of play.

On take-off without any trouble he does 6+3+1 (10) points per round on a 3 point task. He has a good margin of safety. Each round he gets 7 points ahead.

Two rounds into the channel he encounters minor weather trouble -- a mild squall. That is a 20% level task/problem. He now does (55% + d20%) - 20% points per round. He is still safe and still getting ahead. That is, he does 35% + d20% (or 7+d4) points per round into solving the task.

This is the way that a normal harbor exit should go even with minor weather problems. However . . .

Suddenly the spell is dampened as the ship breaks the spar the spell was enchanted to (wood rot that he did not check for after the winter ended). Wavestalker is now in a (30% + d20) - 20% situation. (or 2 + d4)

As the weather worsens with rain(+30% to his problems) he slips into a (30% + d50%) - 50% situation. He is now at d50% - 20% every round and could be losing ground. Add a variable strong wind for a storm and he is at (30% + d100%) - 100% (or d100% - 70% per round).

He is going to start losing that comfortable margin he built up. Luckily for him he makes it back to the dock before things get too sticky.

Reading a foriegn language

Starstrider gets everything fixed and docks at Helvitia. He speaks 15% of Helvitian. With his skill he goes into a cheap restuarant and takes a menu.

A simple menu will take d6-0 points to read. It will (due to formating) have d3 points of "armor" (Starstrider will never read some difficult menus). As long as his dinner companion doesn't stress him (10% as a level one stress) he will do his 3 points a round until the menu is read (or he gives up and guesses). He reads the menu (which took 3 points to understand, and which had 1 point of armor) in two rounds.

Climbing a cliff

Later he is climbing a bit of cliff. He's in a hurry since he dropped his sword and the wolves are getting closer. He has a skill of 20% and climbing equipment worth 20% points. The cliff with wolves is a 20% problem and because of the shale he has to do 2 points before it starts to count (2 points armor on the problem).

This cliff takes two points per meter to climb.

Lets put the numbers together. (20% + {tools} 20% + d20%) - 20 every round. He does 4 + d4 points every round. He rolls a 10 on d20% resulting in 6 points earned (less the 2 points of armor the cliff has from the shale problem). This gets Wavestalker 2 meters up the cliff before the wolves arrive.

Had he been a bit more rushed this would have made a good 100% problem with him at (20 + 20 +d100%) -100% per round. At d100% - 60 he would have probably been caught by the wolves.

He'll need to continue to be careful as he climbs higher so that he doesn't earn negative points, but at 2 meters he is safe until help arrives.


Note that the armor idea solves many theoretical of problems where low-skilled types can't solve that kind of problem at all but high skill types can do it quickly and easily. Take a task with 10 points of armor and 1 task point. If your skill is 45% you'll never succeed. With a skill of 55% you'll do it every time when not under pressure and eventually even with pressure.

These kinds of situations and results are relatively common in real life.


If you want fumbles, you can use a roll of 01% to 05% and a result of negative numbers to mean negative results to the extent of the negative numbers generated. This means that when a highly skilled individual klutzes the results won't be as bad. This is true to life. A highly trained swimmer who slips up gets a mouthfull of water, a neophyte starts to drown.

In addition, the more difficult the situation, the more likely bad results are to occur. In a 100% situation bad results are alot more likely than in a 10% situation. A positive number (even with a 01%) means that the bad result was just a slow result (i.e. you rolled a 01% when you could have rolled higher).


Note that using this system a character is freely transferable between this and any d20/3d6 skill resolution system (like Pendragon). Characters are easily transfered between this and %tile systems. For %tile systems, just use the same numbers. This system is transparent to characters under RUNEQUEST.

Any number (vs %tile) skill is multiplied times 5% to get the percentile skill. I.e. a Pendragon sword skill of 5 becomes 25%.

This allows for simplification when you do not desire the extra complications of this system, and detail when you want to know just how long it will take to pick that lock or climb that cliff.


d100 is the base range. d100 divided by two is d50. d50 divided by two is d25. d25 divided by two is d12. d12 divided by two is d6. Note also that d25 is fairly close to d20 and d12 is fairly close to d10.

Commonly, difficulties are done on d10, d20, d50 and d100. Extremely difficult situations (such as simple heroquests) call for 2d100. Trancendentally difficult situations (such as deep heroquests, etc.) call for 3d100 or 4d100.Note that for a skill of 200% and no difficulty modifiers (4d100 + skill) minus (400 + difficulty) gives an average result of (400 - 400) 0 or a 50/50 chance of success. At just d100 difficulty and skill levels of 300 on both sides the chance of success is still 50%. The system handles both high percentage of success and high levels of difficulty very well.

Back to the storyline now:

Monsters to meet in the forest (encounter chart):

  1. Running Ones
  2. Tiev Gnack
  3. Spiderqueens
  4. Various of the dominated
  5. Lesser Dires
  6. Wraiths and dark elves.

More of those to meet later, and other kinds as well.

Terrain types:  the wilderness heading into Finland from the Rusk city.

Copyright 2005 Stephen R. Marsh and Heather N. Marsh
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