= Quadratic-inflation field interval from a wavenumber interval
{title2=$\Delta\Phi/M_{\rm Pl}\simeq2\Delta\log k/\sqrt{4N+2}$}
For a quadratic <inflaton> potential ending at the leading estimate $\epsilon_V=1$, $\Phi/M_{\rm Pl}=\sqrt{4N+2}$. <Cosmological horizon exit> gives $d\log k/dN=-1+\epsilon_H$. A narrow logarithmic interval therefore probes a field span $2\Delta\log k/(\sqrt{4N+2}(1-\epsilon_H))$, to the accuracy of the <slow-roll approximation>. At sixty e-folds, five logarithmic wavenumber units probe about $0.64M_{\rm Pl}$ around a background field near $15.6M_{\rm Pl}$.
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