EN
Some basic theorems and formulae (equations and inequalities) of several areas of mathematics that hold in Bernstein spaces $B_σ^p$ are no longer valid in larger spaces. However, when a function f is in some sense close to a Bernstein space, then the corresponding relation holds with a remainder or error term. This paper presents a new, unified approach to these errors in terms of the distance of f from $B_σ^p$. The difficult situation of derivative-free error estimates is also covered.