The asymptotic expansion of the function $Z(t)=e^{i\vartheta(t)}\zeta{(1/2+it)}$ for real $t\to+\infty$ where $\vartheta(t)=\Im\log{\Gamma{(1/4+it/2)}}-(t\log{\pi})/2$ – today known as Riemann–Siegel formula – is derived ...