Back then, Gygax developed a system of Non-Weapon Proficiencies for AD&D to keep up with the market. As it turned out, Gygax' system was inelegant, but the most in-depth.
To fully appreciate Gary Gygax's genius and contribution, you have to realize that the original Dungeon Master's Guide was not meant to be read from cover to cover. Instead, it is a reference, out of which the DM plucks an article on the aspect of the DMing that he needs help with, and he gets a useful game mechanic or two, to adjudicate the play. In keeping with this style, each skill, or a NWP or the Non-Weapon Proficiency was a mini-game to cover that particular skill, say, make a suit of armor. You ran through the mini-game, made a few rolls, and whoala!!!
The key difference between the Gygax' Non-Weapon Proficiencies and the Current WHATSIE skill system, as well as the use of skills in Traveler and Rune Quest, is that with Gygax, the Non-Weapon Proficiencies are Cardinal Trait, while in the skills systems that dominated the other games and which WTC adopted, the skills were an Ordinal Trait. What is the difference? Cardinal traits are those few, which define an individual and make him unique. Ordinal traits, are the traits which we all have, but which are developed to a different degree in each person. In game terms this means, that with an ordinal skill, say Horsemanship, you roll for success every time the player character gets on a horse. That's when you start categorizing common tasks and assigning difficulty factors to everything, further complicating the game process. With Cardinal Traits, you only roll, when your character's skill will make a difference. You only roll when a horse tries to throw you, where those unskilled in horsemanship will get thrown, and only the successful use of the skill will keep you in the saddle.
In my campaign, I married the elegance of the Rune Quest skill game mechanic with the narrative power of Gygax's Non-Weapon Proficiencies. Here is how it works:
Let’s say Brent is a WWII Commando being parachuted into Burma. For our purposes he has a Parachute Jump skill of 43%. Brent must roll 43 or less on percentile dice to use the skill successfully.
Initial skill percentage is usually calculated by taking one of the character’s attributes and modifying it by +/- 5,10, or 15 percent based on second requisite. Every time the skill was used successfully to influence the outcome of the game, there is a chance of improvement in that skill. This means that
i) You only roll when a layman will fail and only a skilled person can succeed.
ii) You only have a chance of growth (improvement in that skill) if you make a positive difference in the game – i.e. your First Aid skill saves someone from choking or bleeding to death, if you shoot someone, you shoot and kill a mass murderer shooting up the office, etc.
Only THEN your skill has a chance of improving. i) comes from the initial conceptualization of Non-Weapon Proficiencies by Gary Gygax. ii) is the game mechanic from Runequest.
Every time you roll a skill, you have five possible outcomes: Critical Failure, Fumble, Failure, Special Success, and Critical success. 00(100) on percentile dice is always a fumble or critical failure. 01 on percentile dice is always a special or critical success.
Whenever a skill is rolled, it can be modified up o down in five percent increments based on if you have tools, help, materials and conditions.
Let’s now look at Brent the OSS operative in 1942 Burma. He is jumping on a stormy night onto a clearing on the edge of the jungle.
Success or failure for the skill percentile base 43 is as follows:
01-02 Critical Success
03-09 Special Success
100 Critical failure.
Referee decides that because parachute jumping is inherently a hazardous activity, player must roll his skill to see if there are any problems during the jump. Critical success means that character does not get wet feet and all in order. Special success means that character gets wet but all is okay. Success means character rolls in mud, as can be expected, needs a change of clothing before he can sit at the dinner table, but is otherwise all okay. Failure would mean that character lands okay, but equipment gets wet, maybe some water damage. Failure would mean a messy landing, maybe a sprained ankle, maybe the character got dragged by the parachute through the mud and got messed up and will have to spend time getting his stuff together. Fumble would mean that character has drifted over the jungle. Character must roll his skill again, and if he fails, he gets a broken leg. Critical failure means that the parachute did not get open or it was torn up by the gale force winds inside the storm clouds. Character must roll successfully on his skill or die.
In our case, Referee decides that because of the night and the rain, and the wind the skill roll must be rolled at a -10% penalty. Brent has Parachute Jumping at 43%, he must roll 33 or less to succeed, but the chances for special success or failure remain the same as for the 43% skill!
In our case: Roll 1 = 13!
Brent jumps and lands okay!
After the raid on the Japanese radar outpost, Brent gets a chance to improve in his parachute jumping skill: He must roll 44 or above to have a chance of improvement.
In our case: Roll 2 = 77!
Brent learned from his experience and got better!
When characters get to improve, they get to add 1d6 percentage points to the skill.
In our case: 1d6 Roll 3 = 6!
After the adventure, Brent’s Parachute Jumping skill is 43+6=49%!!!
Importance of Teachers
What are your odds of improving if you skill climbs up to 80 or 90%? Very little. 10% chance per adventure. That’s when you find a good teacher. Based on his teaching skill, his expertise, how well you hit it off, a teacher can add from +5% to over +20% to you “see if you learn from experience” roll.
Great instructors can be hard to find and expensive. That’s part of the game world.
Skill as a d20 Roll
Any skill can be represented as a D&D “Ability Roll” simply by dividing it by 5. Usually this gets done, when a skill is used in place of a common action. Thieves have a hide in shadow ability, so can anybody with common sense. Where does thief benefit from his skill? You say.
When an unskilled character tries to hide in shadows, an ability check versus AGILITY is done (Agility is Dexterity modified by Strength score). Whereas an unskilled character does an ability check and then succeed or fails, a Thief gets to do an ability check, and if THAT fails, then rolls against his Thief’s Ability to Hide in Shadows. Also, while everyone can hide behind some bushes near a campfire and strain to overhear SOME of the conversation, a Thief can use his skill to hide right near the flames and hear ALL of the conversation.
If Brent the paratrooper tried to teach parachute jumping to another soldier, his 43% skill would translate to 43/5= 8 3/5ths=8, with an ability score of 8, Brent would contribute a -5% penalty if he tried teaching anyone the parachute jump!