A method is disclosed for use in design of a system, the system to include a plurality of sources contributing to a variable system effect. The method includes determining a plurality of functional units to form the system, obtaining a plurality of constant functional unit source informations, determining at least one variable quantity, associating each functional unit with one of the at least one variable quantity, obtaining variable functional unit source information by combining the constant functional unit source information with the variable quantity associated with the functional unit, and deriving the variable system effect based on combining the variable functional unit source informations. Further a device for use in design of a system is disclosed and also a tangible computer-readable medium storing instruction code thereon, that when executed causes one or more processors to perform steps for design of a system.