where Ω Ω ( E ) is the number of quantum states in a small interval between E and E + δ δ E . Here δ δ E is a macroscopically small energy interval that is kept fixed. Strictly speaking this means that the entropy depends on the choice of δ δ E . However, in the thermodynamic limit (i.e. in the limit of infinitely large system size), the specific entropy (entropy per unit volume or per unit mass) does not depend on δ δ E .