NcL    Enter number of layers for region c (between 1 and 9).
        Set c to T for top, M for middle and B for bottom.

 AcL    Add a layer between existing layers in a region.
        Set c to T for top, M for middle and B for bottom.

 RcL    Remove a layer between existing layers.
        Set c to T for top, M for middle and B for bottom.

 CL     Copy parameters from one layer in any region to another layer in
        any region.

 NMR    Enter the number of repeats of the middle region to make a
        superlattice.  Note: the bottom of the top region and the top of
        the bottom region must each be set to one repeat if NMR is
        greater than 1 for the profile to be constructed correctly.

 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.

 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.