“…In the last 15 years e + e − cross-section measurements have dramatically improved, from energy scans [27][28][29] at Novosibirsk (NSK) and later, using the radiative return mecha- nism, measurements via initial state radiation (ISR) at meson factories (see figure 4) [30][31][32][33][34]. A third possibility to enhance experimental information useful to improve HVP estimates are τ -decay spectra τ →ν τ π 0 π − , · · · , supplied by isospin breaking effects [5][6][7][35][36][37][38][39][40]. In the conserved vector current (CVC) limit τ spectra should be identical to the isovector part I = 1 of the e + e − spectra, as illustrated in figure 5.…”