AL     Add a layer between existing layers.

 CL     Copy parameters from one layer to another.

 RL     Remove a layer between existing layers.

 SL     Create a superlattice from a specified range of layers.

 NL     Enter number of layers (between 1 and 124 as of this writing ).

 NP     Enter number of data points (automatically done by GD).

 NR     Enter number of layers used to simulate rough interface (greater
        than 2).

 PR     Enter profile shape for simulated roughness.

 PS     Enter polarization states to use.

 QL     Enter Q limits of data set (automatically done by GD).

 BI     Enter intensity of incident beam (multiplies calculated
        reflectivity to give count rate).

 BK     Enter constant background intensity added to calculated
        intensity.

 DL     Enter the wavelength divergence of the incident beam (in
        Angstroms) to be used in the resolution convolution.

 DT     Enter the angular divergence of the incident beam (in radians)
        to be used in the resolution convolution.

 VMU
 MUV    Enter the length absorption coefficient of the vacuum.

 VQC
 QCV    Enter critical Q squared of the vacuum.

 VQM
 QMV    Enter magnetic critical Q squared of the vacuum.

 WL     Enter wavelength of incident radiation.