Confidence level (Co) that structure is an impact crater. Possible values are 1 (almost certain, 80 to 100% confidence), 2 (probable, 30% to 80% confidence), and 3 (cannot be ruled out as an impact structure, <30% confidence). Confidence levels are subjective, but are generally based on the presence or absence of such features as "hummocky" ejecta, well-defined ejecta deposits, rough walls, terracing (larger craters only), and a central peak or peak ring (larger craters only). Volcanic structures, the features most often confused with impact craters, usually are steep-sided, have smooth inner walls, and have smaller, less complete (if any) ejecta deposits than impact craters.