  We provide a set of sum rules relating CP-averaged branching ratios and
CP-asymmetries of the $B \to \pi K$ modes. They prove to be useful as a
mechanism to `test' experimental data given our expectations of the size of
isospin breaking. A set of observables emerges providing a simpler
interpretation of data in terms of isospin breaking. Moreover, the derivation
is done in a completely model independent way, i.e., they can accommodate also
New Physics contributions.
