See comments for problems encountered in the following code.
s2 is Single returned from selecting a space within the overall selection to
be acted on, and reading its font.spacing, and s3 = s2 before any changes are
made to s2. Problems are found when this is (correctly) read as -0.65
Is the problem derived from manipulation of minus numbers? It is rather
difficult to program when incorrect values are returned by the program. Or
what am I missing here?

'       Replaces spacing of spaces in selection with new spacing
       Call ClearFormat
       With Selection.Find
           .Text = " "
           .Font.Spacing = s2 ' But Font.Spacing is here returned as -0.6
           .Replacement.Text = "^&"
'      The following complicated line (used also previously in code)
attempts to prevent more than one decimal place being assigned to the
font.spacing amount. However, the font.spacing is still at -0.65!
           .Replacement.Font.Spacing = 0 - Fix(10 * (Selection.Font.Size /
b2)) / 10
           .Wrap = wdFindStop
           .Execute
'           The following code is because VBA does not return the correct
values;
'           the returned numbers here are still not correct, but it seems to
work.
'           Word has a particular predilection for -0.65 as a reduction,
even when
'           it has not been called for or determined by the program.
           If .Found = False Then
               
               If s2 <= s3 - 0.05 Then
                   s2 = s3 + 0.05
                   GoTo 50
               End If

               If s2 >= s3 + 0.05 Then GoTo CollSel

               s2 = s2 - 0.05
               GoTo 50

           End If
           
           Do While .Found = True
               .Execute Replace:=wdReplaceOne
               rngOriginalSelection.Select
           Loop
           
       End With