Table 1: Error levels and feedback design.

Error level		level 1	level 2	level 3
Error distance ε (cm)		0.5≤ε<1.5	1.5≤ε<3.0	3.0≤ε<5.0
Category	Target	Output
Visual feedback	Color of brush handle	yellow	orange	red
Auditory feedback	Sound tempo	slow	moderate	fast
Haptic feedback	Intensity of vibration	weak	moderate	strong