The term $D(q)$ provides a new means of comparing damage simulations to experiment, and testing the assumptions that underpin damage models for the single molecule case.

For low diffraction intensities, the dominant error in the calculation of $D(q)$ from experimental data is the error of $\mu_\textrm{pix}(q)$, given by $$\begin{aligned}
\delta \mu_\textrm{pix}(q) = \frac{\sqrt{\mu_\textrm{pix}(q)}}{\sqrt{N_\textrm{DATA}} \sqrt{M(q)}}\;,\end{aligned}$$ where $N_\textrm{DATA}$ is the number of diffraction patterns recorded. The term $M(q)$ is the number of speckles in resolution ring $q$, which is estimated by dividing the circumference of the ring by the expected speckle width $\frac{1}{d}$, where $d$ is the width of the molecule. Assuming $D(q)$ is of the order of one, the error in $D(q)$ goes like $\delta D(q) \approx |\delta \mu_\textrm{pix}(q)|  /  |\mu_\textrm{pix}(q)| $. For the test molecule quoted above and 8 keV photon energy, 2 mJ pulse energy, $100 \times 100$ nm$^2$ spot size at a resolution of $q = 6.67$ nm$^{-1}$, an accuracy of $\delta D(q) = 0.01$ can be achieved in of the order of $10^3$ patterns, which is an order of magnitude less than the number required to achieve the same resolution in an imaging experiment[@Tegze2012]. This analysis could be used to gain early feedback about the data used 