Select "Help & Options", then "Visuals" and disable the "Clean HUD" option. Select a slow-paced and relatively short song, such as "enV - Bloom". Play the desired song until all hits are "Perfect". After each hit a circle around you will blink with hit precision information. If it is not a cyan "Perfect", restart the song. You will see the number of perfect hits at the end of the song. You do not have to build a perfect combo. Ignore collecting the power-ups and concentrate on perfect hits only.