dynamical change in the sample structure because it will drop relative to the mean scattering signal, as has been shown for averages of molecular conformation [@Maia2009]. To isolate the effect of damage-induced structural change, we create a measure that first subtracts the expected contribution of shot noise, which is equal to $ \mu_\textrm{pix}(q)$, and then normalizes by the mean intensity as follows: $$D(q) = \frac{\sigma_{\textrm{pix}}^2(q) - \mu_\textrm{pix}(q)}{\mu^2_\textrm{pix}(q)} \;,$$ where $\mu_\textrm{pix}(q)$ is the average intensity at a pixel in resolution ring $q$ averaged over the whole dataset and $\sigma_{\textrm{pix}}(q)$ is the corresponding standard deviation. The mean and standard deviation are calculated from the ensemble of experimental data of molecules measured individually in random orientations. It possible to show that $$D(q) \approx \frac{\langle B_{ij}^2(q) \rangle}{ A^2(q)} \;,$$ where $\langle B_{ij}^2(q) \rangle$ is given in Appendix \[sec:app:sigB\]. It is possible to show that $0 < D(q) < 1$, because $\langle f(q,t) f(q,t') \rangle^2 < \langle f^2(q,t) \rangle \langle f^2(q,t') \rangle$. Figure \[fig:pulselength\_g2\] shows $D(q)$ for variations of pulse duration at constant pulse energy (2 mJ). The large variations at high scattering angle indicate the sensitivity of $D(q)$ to ion motion and inner shell ionization, thereby providing complementary information to a measurement of $A(q)$. 