Insisting on the role of experimental data: the pseudoscalar-pole piece to the $(g_{\mu }-2)$ and the $\mathrm{\mid }{V}_{ub}\mathrm{\mid }$ from $B\to \pi \mathrm{\ell }{\nu }_{\mathrm{\ell }}$ 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 $B\to \pi \mathrm{\ell }{\nu }_{\mathrm{\ell }}$ differential branching ratios which allows to determine the $\mathrm{\mid }{V}_{ub}\mathrm{\mid }$ CKM parameter.