Note that W ˙ ˙ l o s t is a relative quantity, in that it is measured in relation to a specific thermal reservoir. In the above equations, W ˙ ˙ l o s t is defined in reference to the environment reservoir, at T 0 . When comparing the actual process to an ideal, reversible process between the same endpoints (in order to evaluate W r e v , so as to find the value of W l o s t ), only the heat interaction with the reference reservoir T 0 is allowed to vary. The heat interactions between the system and other reservoirs are kept the same. So, if a different reference reservoir T r e f is chosen, the theorem would read W ˙ ˙ l o s t , t o t = T r e f S ˙ ˙ g , t o t , where this time W ˙ ˙ l o s t is in relation to T r e f , and in the corresponding reversible process, only the heat interaction with T r e f is different.