Table 2.

Characterization of the uncertainty sources for calibration.

Variable	Estimator	Density Function	Type	Description
Ex	Y	Normal	A	Indication error
u accelref	X1	Normal	A	Reference vibrometer RMS acceleration
u accelsw	X2	Normal	A	Smartwatch RMS acceleration
u tempref	X3	Rectangular	B	Reference vibrometer variation due to the temperature
u tempsw	X4	Rectangular	B	Smartwatch based vibrometer variation due to the temperature
u resref	X5	Rectangular	B	Reference vibrometer finite resolution
u ressw	X6	Rectangular	B	Smartwatch vibrometer finite resolution
u calibref	X7	Normal	B	Reference vibrometer uncertainty
u calibsw	X8	Normal	B	Smartwatch calibration uncertainty
u crosssw	X9	Rectangular	B	Smartwatch accelerometer cross sensitivity
u crossref	X10	Rectangular	B	Reference accelerometer cross sensitivity
u swjitt	X11	Normal	B	Smartwatch RMS uncertainty due to the sampling rate variation