Distinguishing base obstacle from disadvantages

Question

In Burning Wheel, the base obstacle of a test and disadvantages are treated separately.

(By "base obstacle" I mean the obstacle without conditional modifiers; this terminology might not appear in the book.)

The different treatment happens, for example, when there is double obstacle penalty - only the base obstacle is doubled, not the modifiers.

As a game master, how do I decide what is the base obstacle of a test, and what are modifiers? There are obvious cases, of course, but there are also unclear ones. The following are from the orienteering skill, and are just an example - I am not particularly interested in orienteering. Quote heavily edited for brevity.

Day and familiar land, Ob 1; Night familiar, Ob 2; Unfamiliar, Ob 3; Unfamiliar at night, Ob 4; Familiar during storm, Ob 5; Storm at night, Ob 6.

Here, it would be tempting to say that daytime obstacle is the basic one and nighttime gives +1 Ob. Or that a storm gives +4 Ob. Or unfamiliar land gives +2 Ob, etc.

Suppose I want to adjudicate killing a bunch of orcs with a simple weapon skill test. Should I say that that sounds a heroic thing to do, so obstacle is 6, or that killing one would be obstacle 4 and because there are so many, that is +2 Ob?

In general: How do I decide how the obstacle of a test is divided between the base obstacle and disadvantages?

Answer 1

Only explicit modifiers are modifiers

All the obstacles in the skill listings are base obstacles. When using those, they aren't including any disadvantage modifiers. (BWG p. 25 even calls out the obstacles in skill listings as basic obstacles to set.)

When a mechanic explicitly adds a disadvantage modifier, treat that as a modifier and don't include it in a doubled obstacle penalty. For example, when a Duel of Wits maneuver like Obfuscate imposes a +1 Ob on the opponent's next action, that's a modifier and never doubled.

When you're making up your own Obstacles, you have to ask yourself what's base Obstacle and what's modifier. You have to trust that your judgement and understanding of how you're modelling the situation will tell you what you've already decided is a modifier and what isn't. When in doubt: it's all part of the base Obstacle you've chosen, since modifiers are always explicit.

It might help to think of it this way: Disadvantages are increases to the Ob of a test. If you don't know what the Ob being increased is to begin with, then the Ob you're looking at isn't the result of an increase and is just a base Ob.