Fallout How do dialog checks work in Fallout 1/2? What's lockpicking success chance based on?

[deuxhero]

I'm replaying Fallout 2 and I've noticed dialog checks appear to be random, changing between game loads. This seems to apply both to getting a "good" reaction from the same dialog option (telling Whiskey Bob his name means he should be the one providing the booze), and even getting the "advanced" dialog options at all. What's the actual math going on here? What's the size of the "dice" for RNG influence?

Also interested in any other Fallout 1/2 formulas (hit chance, pickpocket, etc.) anyone knows.

 

[agris]

I believe all of F2’s non-attribute checks are fundamentally a d100 check vs your skill level, with the d100 check modified by the intended difficulty of the challenge prior to testing vs your skill.

So, for example, an “easy” lock to pick would be a d100 challenge-50 vs your skill. If the modified roll is equal to or less than your lockpick skill, you succeed.

I believe this is similar to GURPS, due to Fallout using gurps throughout much of F1’s development.