However, the result usually includes terms proportional to expressions like 1 / ϵ ϵ which are not well-defined in the limit ϵ ϵ → → 0 . Regularization is the first step towards obtaining a completely finite and meaningful result; in quantum field theory it must be usually followed by a related, but independent technique called renormalization. Renormalization is based on the requirement that some physical quantities — expressed by seemingly divergent expressions such as 1 / ϵ ϵ — are equal to the observed values. Such a constraint allows one to calculate a finite value for many other quantities that looked divergent.