Take the value of the Attribute
Modify with the value of the Skill
Modify with any circumstance modifiers assigned but the Guide
Modify with the value of a 2d6 - 2d6 dice roll
This results in Degree of Success from -10 to 0 to +10.
A result of 0 to +10 is a Success.
A result of -10 to -1 is not a Success.