  The concept of a modular value of an observable of a pre- and post-selected
quantum system is introduced. It is similar in form and in some cases has a
close connection to the weak value of an observable, but instead of describing
an effective interaction when the coupling is weak, it describes a coupling of
any strength but only to qubit meters. The generalization of the concept for a
coupling of a composite system to a multi-qubit meter provides an explanation
of some current experiments.
