${\varphi }_j$	phase observed by probe j
${\theta }_j$	angular position of probe j
A	blade vibration amplitude
$d_j$	blade displacement measured by probe j
$feo$	fractional engine order
H	number of revolutions
h	revolution number
i	blade number
j	probe number
N	number of blades
M	number of probes
$P_j$	invariant offset for probe j
pk-pk	peak-to-peak amplitude
r	Pearson correlation coefficient (coherence)
$rpm$	revolutions per minute
$unc$	uncertainty
BHM	Blade Health Monitoring
BTT	Blade Tip-Timing
EO	Engine Order
FEM	Finite Element Method
FFT	Fast Fourier Transform
IGV	Inlet Guide Vanes
ITWL	Air Force Institute of Technology in Warsaw
LSF	Least Squares Fitting
M1	1st vibration mode
MDPI	Multidisciplinary Digital Publishing Institute
ND	nodal diameter
NI	non-integral vibrations
NSMS	Non-contact Stress Measurement System