Comparing the Impact of Different Datasets on α_{¹²CO(1−0)} Estimates. We compare the results after substituting feathered H I (left column) and non-feathered H I (right column) observations as well as different ¹²CO(2–1) observations (data from this project and HERACLES). The points show the resulting α_{¹²CO(1−0)} value for the different solution pixels. The black line indicates the binned trend, and the shaded region illustrates the 1σ scatter per bin. The right panel shows the average values of the different permutations (color-coded). The grey point is based on using the ¹²CO(2–1) data only (and deriving the ¹²CO(1–0) data using a fixed R₂₁). This approach reproduced the method by Sandstrom et al. (2013). The solid line indicates the average MW α_{¹²CO(1−0)} value, and the dashed line shows the average value found by Sandstrom et al. (2013) for M101.