The interval used to claculate each slope (default = 21 nm).
r2threshold
The r2 threshold that determines if a slope is "valide".
The default value is 0.8 meaning that the determination coefficient of the
regression between log-transformed data and wavelength should be >= 0.8.
Value
A dataframe containing the centered wavelength, the calculated slope
and the determination coefficient of the linear regression used to claculate
the slope.