Problem with the code

#include <ftmagphase>
Macro AbsorptionMax(name,noise,thickness,index)
    string name
    variable /d noise
    variable /d thickness
    variable /d index
    prompt name "the reference wave name is ?"
    prompt noise "the noise floor level in freq domain = ?"
    prompt thickness "the sample thickness in [m] is = ?"
    prompt index "the THz index of refraction of the sample is ~ ?"
    string freqdomain=name+"_dmag"//creates new wave name
    string destw=name+"_absmax"
    duplicate /O $freqdomain $destw//creates new wave
    //calculates maximum measurable absorption coefficient as described in
    //Jepsen, P. U.; Fischer, B. M. Optical Letters, 30 (1) 29-31 (2005)
    $destw=2*ln(($freqdomain/noise)*4*index/(1+index)^2)/(thickness*100)
    SetScale d 0,0,"", $destw
    display $destw
    Label left "\\Z14\\F'symbol'a\\F'arial'\\Bmax \\M\\Z12 [cm \\S-1\\M\\Z12]";DelayUpdate
    Label bottom "\\u#2\\Z12 Frequency [THz]"
    SetAxis bottom 0,1e+13
    SetAxis left 0,*
    ModifyGraph rgb($destw)=(0,0,0)
Endmacro