Photometric variability in cataclysmic variables (CVs) on time scales longer than a few days can be most effectively addressed by automated long-term monitoring programs such as that of RoboScope (Honeycutt & Turner 1992): more than 100 CVs have been monitored for about 13 years, obtaining 75 to 150 measurements per year for each system. Among the techniques being explored for analysing this data set is the use of the structure function (SF), an autocorrelation tool employed extensively for the study of the light curves of AGNs (e.g. Hufnagel & Bregman 1992). A first order SF measures the scatter in a time series of magnitudes, m, as as a function of the time lag, τ (Hughes, Aller & Aller 1992).