As a result of applying the previous steps, one obtains a fuzzy set from the reasoning process that describes, for each possible value , how reasonable it is to use this particular value. In other words, for every possible value , one gets a grade of membership that describes to what extent this value is reasonable to use. Using a fuzzy system as a controller, one wants to transform this fuzzy information into a single value that will actually be applied. This transformation from a fuzzy set to a crisp number is called a defuzzification. It is not a unique operation as different approaches are possible. The most important ones for control are described in the following.