Some vector mesons can, compared to other mesons, be measured to a very high precision. This stems from the fact that they have the same quantum numbers as the photon, J = 1, where J = angular momentum quantum number, P = parity, C = C parity. Therefore they appear in electron-positron collisions in the process e − − e + → → γ γ → → q q ¯ ¯ , which provides experimentally a clear signal compared to other measurements, which have to use hadronic processes. Vector mesons play a huge role in the study of the strong hadronic force.