$m_i$	The ith spectral moment
${\alpha }_{i }$	Spectral width
$E\left[P\right]$	Expected occurrence of peak
$E\left[0\right]$	Expected rate of zero crossing
$\gamma$	Irregularity factor
$P_x$	Probability density function
x	Variable load
$\overline{\mathrm{x}}$	Mean
Nf	Data sample size
$N\left(S\right)$	Number of stress cycles expected per second
$S$	Probability density function of stress range
erf	Predicted rain flow count per second
$D_{\mathrm{i}}$	ith function of spectral moments
R	Function of spectral moments