List complementary functions = level 1 and level 2
Functional analysis: expressing needs in terms of functions and methods for finding functions

Transform all the desires expressed by the user into an action or benefit (service rendered by the product). Use a verb and a complement.

List the actions to be performed by the product or system one by one.

The basic principle is as follows:

• the object studied has functions only in use;

• the functions of an object are independent of the solutions that realize them;

• an object's functions are independent of each other.

Example 1: "Redesign" of the "refillable flint gas lighter" - service functions

The service functions in use are :

• ignite a gaseous mixture;

• use one hand ;

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