Nomenclature
$X$	degradation variable	$t$	degradation time
$D$	distance	$\mu$	mean value
$s$	standard deviation	$\rho$	normalized area metric
$A$	the area between function and x-axis	$K$	probability density function
$I$	interval number	$T_o$	vector of observation instants
o	number of observation instants	m	number of experimental samples
$P_r$	pre-set threshold	$P$	probability function
$T_C$	total cost of validation experiment	$C_u$	cost of an experimental sample
$C_m$	cost of an experimental observation	$C_p$	labor cost and public resource cost of a sample in a unit time
Subscript
e	experimental data	s	simulation model
$\underset{\_}{}$	lower bound of interval number	$\overline{}$	upper bound of interval number