Get the size of a sector on a drive.
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 Syntax

        GT_SectSiz([<ncDrive>]) --> nSectorSize

 Arguments:

      <ncDrive> is an optional parameter that is the id of the drive
      to be read. This paramater can be either a character value who's
      first character is taken as the drive letter or a numeric value
      where 0 = Default, 1 = A:, 2 = B:, etc... If no parameter is
      passed the default drive is used.

 Returns:

      The size of a sector on the drive in bytes. If the drive is
      invalid the return value will be -1.

 Description:

      GT_SectSiz() can be used to find the size in bytes of a sector
      on a disk.

 Examples:

      // Each of the following print the size of a sector on drive C:

      ? GT_SectSiz("C:")
      ? GT_SectSiz("C")
      ? GT_SectSiz("Clipper")         // First letter is used only.
      ? GT_SectSiz(3)

      // The next two print the size of a sector on the current drive.

      ? GT_SectSiz(0)
      ? GT_SectSiz()

 Source: SECTSIZE.C

 Author:  Dave Pearson