Comparison of CO estimates from Planck Type 3 CO maps and ground-based observations. Upper frame compares the sum of ¹²CO(2–1) and ¹³ CO(2–1) values of 56 SMT maps to Planck CO estimates for the assumed line ratio of (2−1)/(1−0) = 0.5. Lower frame shows comparison with CO(1–0) observations from the PMO telescope, with data at 7′ resolution sampled at 3′ steps. Each colour and symbol combination corresponds to one of 17 fields. Solid lines show the one-to-one relations, and dotted lines correspond to slopes different by ±30%.