= Solution
Write $V_{\rm in}=v(t)+V_{\rm off}$, with constant unwanted offset $V_{\rm off}$. Add an adjustable reference <voltage> $V_b$ through another <resistor> $R_b$ to the \b[first] inverting summing junction, as the dashed branch in the circuit figure shows. <Kirchhoff's current law> now gives
$$
V_1=-R_f\left(\frac{V_{\rm in}}{R_a}+\frac{V_b}{R_b}\right).
$$
Choose the reference polarity and magnitude so that
$$
\boxed{\frac{V_b}{R_b}=-\frac{V_{\rm off}}{R_a}.}
$$
A potentiometer between positive and negative reference supplies permits either sign. The first stage then has zero output <voltage> when $v=0$, and the <op amp integrator> integrates only $v(t)$:
$$
\boxed{V_{\rm out}(t)=V_{\rm out}(t_0)+\frac{R_f}{R_aR_iC_i}\int_{t_0}^t v(t')\,dt'.}
$$
Merely placing a large <resistor> across the integrating <capacitor> limits drift but also changes the <transfer function>; cancellation at the summing junction preserves ideal integration of the desired signal.
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