from the Winisis "reference" manual:

$
i. Gizmo conversion table
	This  field may contain the name of a Gizmo conversion table to be
	used   for   import.  This  facility  is  provided  to  facilitate
	interchange of text containing diacritical marks between different
	hardware and/or software platforms. A gizmo conversion table is an
	ASCII  text  file,  which  you  may create using any familiar text
	editor, and is defined as follows.
	The  first  character  of  the first line contains the diacritical
	prefix  (normally  the  @ sign for CDS/ISIS). Each subsequent line
	has the following format:
	dxyxyxyxyxy....xy
	where  : d is the diacritical code (e.g. 7 for acute accent), x is
	the character to be accented, and y is the accented character.
	A sample gizmo conversion table is given below:
	@
	6aàeè
	7aáeé
	(([
	))]
	CDS/ISIS uses this table to provide encoded diacriticals on export
	(e.g.  é  will  be  converted  to  @7e),  and  to  decode  encoded
	diacriticals  on  import (e.g. @6a will be converted to à). When a
	Gizmo  conversion  table  is used for import, CDS/ISIS will simply
	strip  the  diacritical for all those characters not listed in the
	table.  For example, using the table given above, the input string
	@7e.  will  be  converted  to  é,  whereas  the string @7y will be
	converted to y, because y is not listed in line 7.
	Note: this feature is not implemented in this version.
$


at some (?) other source i found:

$
a gizmo is a masterfile containing text replacements.
gizmo records have fields with tags 1 and 2.
every occurence of the contents of field 1 is replaced
by the contents of the associated field 2.

gizmo translation can be used
- to perform charset translation, e.g. Cp850 to ISO-8859-1
- to translate special chars like <> with something nicer like /
- to htmlify output like with < to &lt;
- to replace certain keywords that might be used in field contents

if a gizmo record has a field 11,
and it contains the three characters:
- asc	then field 1 is used as decimal number giving a char value
- hex	then field 1 is used as hex number (e.g. d7) giving a char value
in the same way field 21 may control interpretation of field 2.
$