In many cases, it is preferable to use a slightly modified version of the Gouy-Stodola theorem in work form, where T 0 is replaced by some effective temperature. When this is done, it often enlarges the scope of the theorem, and adapts it to be applicable to more systems or situations. For example, the corrections elaborated below are only necessary when the system exchanges heat with more than one reservoir - if it exchanges heat only at the environmental temperature T 0 , the simple form above holds true. Additionally, modifications may change the reversible process to which the real process is compared in calculating W ˙ ˙ l o s t .