GURPS 4 House Rules
Section 9 - Skill Rolls

HR9.1 Reaction Rolls - B494, B559

Reaction Rolls, where the GM wishes to use it, are like Success Rolls of Charisma-2 but the reaction equal or lower than the margin of success or failure is found in the table below.

Reaction Roll Reaction
+6 Excellent
+3 Very Good
0 Good
-3 Neutral
-6 Poor
-9 Bad
-12 Very Bad
-15 Disastrous

HR9.2 Influence Rolls - B359

HR9.3 Assess rolls

Characters who are experts in their field can often predict the difficulty of a future Success roll beforehand, rather than finding out the hard way as they do it. At the GM's discretion, a character may spend a few minutes investigating the subject or environment in effect. This could be visually inspecting the subject, using diagnostic equipment or reading some recent, reliable reports. This is useful for deciding whether to bother with lengthy tasks or where failure would be disasterous.

The character must be trained and only applies if the subject or environment doesn't change by the time the task proper is attempted. It does not apply to combat skills or Contested skills against other people where the situation is too fluid and unpredictable.

Assess rolls are 1d+10 compared to the characters effective, IQ-based skill level. Assess rolls are not Success rolls and critical success and critical failure do not apply. An effective skill level of 16 or better is an automatic success. If successful, the GM permits the following:

The two dice results are recorded until the GM decides the situation has changed or the character has forgotten what he discovered. If the player subsequently decides to make a Success roll, he only rolls the 1st die and combines it with the known results.

As a convenience, the probabilities of success are shown below.

Skill Level Probability of Success
Assess roll
10 or less Failure
11 16.7%
12 33.3%
13 50.0%
14 66.7%
15 83.3%
16 or more Automatic

Example: The PCs were attacked by a Mafia hit squad on an open road and though they were victorous, the car is disabled. Fearing a second hit squad, the party would rather disappear into the fields if repairs would take too long. So Sean pops the hood and pores over the engine and underside for 2 minutes. With Mechanic (Automobile)-17, the Assess roll is automatically successful and Sean rolls 1 and 3 for the future Success roll and is told that his toolkit means 1.5 hours work at no modifiers if the rest of the party helps with lifting. Even in a worst case scenario (rolling 6 for the 1st die), the GM agrees a 10 is a 5 margin of success and 50% cut in time. At best (rolling 1 for the 1st die) and critical success (5), the time would be cut by 95%. The party was lucky the damage was so light.

Example: The PCs need to intercept a scout ship with stolen evidence. They know where it's heading but it has a 5 hour head start. David Winchester, the veteran navigator, investigates the chance of using a shortcut in hyperspace without getting lost. With Navigation (Hyperspace)-16, David knows how to read the hyperspace, turbulence reports available from gateways at both ends but there is no midway report. Such a lack of information means a -3 penalty and the Assess roll is no longer automatic but David succeeds. He rolls 6 and 2, indicating slightly unfavourable navigation, and is told 10 hours travel time to catch up those 5 hours. Even at worst, he can afford a -1 penalty to shave 10% off the travel time.

Example: Pierre needs to break into the offices of Brogden and Wiley at night but wants to research the door security. The GM declares he must inspect the security close up and make an Observation to avoid attracting attention. Pierre is allowed a Traps Assess roll to inspect the door sensors that are visible through the glass door but a -6 penalty to Lockpicking Assess as the electronics of the card reader is under cover.