ACE SWEPAM solar wind ion speed measurements (red dots) and pressure corrected 3D ballistic solar wind speed (blue dots) in 2017 with a temporal resolution of 3.6 h (a). Non-corotating effects such as ICMEs were removed from the datasets. The correlation coefficient (b) and the root mean square error (c) are shown with a sliding window of one Carrington rotation between the ACE solar wind speed and the pressure corrected (black dots) and the non-pressure corrected (grey dots) ballistic solution.