The # indicates that the data will come from the external file rather than data defined as part of the dynamic input.
The name of the file on your PC would be something like DLF_Spectrum.txt. It contains two simple columns separated by at least one space holding the DLF vs frequency data. The # is not part of the file name. Instead the # is used in the CAESAR II input to indicate that the data comes from the external file.
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Dave Diehl