[sir_pudding]

Originally Posted by korbeau

The PC engineer is from Britannica-6 and he's trap in Yrth and want to build a motor for a boat

This, I wouldn't use Invention for, if he's building an engine of a type he's seen before.

and in my other campaign, we are in a WWII universe trying to build a better motor.

This, though, is invention.

We play realistic but it include some fantastic elements.. anyway, for now I'm more preoccupy about the +4 easy skill vs mundane skill you raised earlier.

The relevant rules are on p. B345, and you'll note both the section you've quoted from How to Be a GURPS GM and B171 reference that section for the full rule.

For a specific example of this sort of thing as it applies to firearms see the Non-Combat bonuses box on GURPS Tactical Shooting p. 9.

Note that none of these give bonuses for not being chased by zombies, or anything of the sort, but rather give bonuses for being in a low stakes situation with few variables and a controlled environment.

Some people seem to think this means that you should be able to say "My character is a robot with Unfazeable and he doesn't care if zombies are chasing him, therefore he always gets +4 to +10 to everything he does for free!" This doesn't make a lot of sense, because most of the reason you get that bonus isn't because you are afraid of zombies, it's because you are working in an environment that doesn't have chaotic completely unpredictable dangerous stuff happening that you need to be able to react to, and where if you accidentally drop something on the ground you can just pick it up without having to make a bunch of Change Posture maneuvers while a orc brains you with his axe. A robot repairing the same problems with cars everyday in a well organized, well lit, and well appointed garage in a quiet business park is going to benefit from the predictable task and environment the same as a person. The robot shouldn't get to treat fixing a car in a mud pit, at dusk, while being mortared, as "easy" just because it's "not scared of mortars" because that doesn't have anything to do with most of the ways mud, shrapnel, and dusk aren't like that quiet garage.

Easy tasks are easy, because generally all of: the consequences of mistakes are correctable, the environment is totally controlled and perfectly adequate, there are no variables that make the task impossible to predict, and there are no massive distractions that make it impossible to fully concentrate on it, are true.

Inventing something wholly new, has mistakes with large uncorrectable consequences (loss of staggeringly huge sums of money; lab explosions) and the entire project is a series of totally unknown variables.