Table 1.

Technical properties of different existing smoothness measures

Measure	Validity			Sensitivity	Reliability	Practicality
	D	M1	M2		Measurement noise
Root mean square jerk	×	-	-	-	-	✓
Normalized mean absolute jerk	×	-	-	-	-	✓
Dimensionless jerk	✓	✓	✓	×	×	✓
Log dimensionless jerk	✓	✓	✓	✓	×	✓
No. of peaks	✓	✓	✓	×	×	✓
Speed arc length	✓	✓	✓	✓	×	✓
Spectral arc length
(SAL introduced in [4])	×	✓	✓	✓	✓	✓
Spectral arc length
(SPARC introduced in this paper)	✓	✓	✓	✓	✓	✓

D - Dimensionless; M1 - Monotonic response to changes in submovement interval; M2 - Monotonic response to changes in number of sub-movements. (× means the measure does not satisfy this property, $✓$ indicates that it does satisfy the property. − indicates that information about this property is not available)