Insisting on the role of experimental data: The pseudoscalar-pole piece to the (g_µ − 2) and the |V_ub| from B → π`ν<sub>`</sub> differential branching ratio

We employ a mathematical framework based on rational approximants in order to calculate meson form factors. The method profits from unitary, is systematic and data based, and is able to ascribe a systematic uncertainty which provides for the desired model independence. Two examples are discussed: the transition form factor entering the pseudoscalar-pole piece of the hadronic light-by-light contribution to the anomalous magnetic moment of the muon, and the B → π form factor participating the B → π`ν<sub>`</sub> differential branching ratios which allows to determine the |V_ub| CKM parameter.