Insisting on the role of experimental data: the pseudoscalar-pole piece to the $(g_mu-2)$ and the $|V_{ub}|$ from $B to pi ell u_{ell}$ 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 $B to pi$ form factor participating the $Btopiell u_{ell}$ differential branching ratios which allows to determine the $|V_{ub}|$ CKM parameter.