Well all my rules are a In House system that is based off of Clasic Traveller that I have been using now for 20 years.
My skill system is a basic 10 levels system that also has a Level 0
I use a D100 % skill roll system
Every skill takes the following
Add together Two character attributes scores to obtain the base score.
Ex: Say some skill required INT and EDU, and the character had a INT9 and EDU of 10/ Thus (9 + 10) = Base score 19 on d100 percent
Then if someone has a Level 0 skill they get a +10% added to their chance of success. Example (9 + 10) + (10) = 29 on d100 percent
Modifiers are as follows:
 Simple task: +2 ...aka...+10% added to the base
 Standard Task: +0 ...aka...No modifier to the base
 Hard Task: 3 ...aka...15& subtracted from the base
 Extremely Difficult Task: 5 ...aka...25% subtracted from the base
 TL difference: +/2 ...aka...+/10% for each TWO levels different than the players base TL.
NOTE: For each Level in a skill gained a player gets +5% added to their Base percent chance of success
I have used this system for many many years and it works rather well in my game and players seem to be able to grasp it quite well and it runs smoothly to GM as well too.
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Long time Old Traveller Gamer and Game Master circa 1976
