Page 5 likely to yield the most reliable results. Kirchoff et al. (2011) provide a more recent comparison with three researchers (two expert, one novice without crater counting experience) from the same lab who used the same technique to identify, measure, and, in this case, classify craters by preservation state. They used Lunar Reconnaissance Orbiter Camera Wide-Angle Camera (LROC WAC) images of Mare Orientale. The two experienced analysts had counts that differed by 20-40% in a given diameter range, while the novice counter identified numerous features that are probably not craters, differing from the other two by >100% over some diameter ranges. They also had significant variation among the preservation states attributed to each crater, despite a relatively coarse fourpoint scale. This work showed that despite common thinking that crater counting is fairly easy and straightforward, there is a learning curve and an individual's crater counts should be discarded during the learning process. It also showed that even well defined crater morphologies may be difficult to classify uniformly. Hiesinger et al. (2012) also focused on lunar craters, in their case using LROC Narrow-Angle Camera (NAC) images at approximately 0.5 m/px. They were interested in reproducible results for better understanding the lunar cratering flux and performed a single test with two experienced researchers who used the same technique on the same image. The Heisinger et al.(2012) team found an overall variation of only ±2% between their analysts, a dispersion significantly less than previous work.What this brief review indicates is that while there has been some discussion in the literature about agreement between different researchers' crater identifications, (a) there has been no thorough discussion on researcher variability, (b) no published study discusses the variability when using different techniques for crater identification and measurement, (c) variation in crater morphology has not been discussed (e.g., sub-km craters appear substantially different at NAC pixel scales when compared with multi-km craters at WAC pixels scales), and (d) expert results have not been extensively compared with how well untrained or minimally trained crater counters do with the identification and measurement process. Given the proliferation of internet

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