Carol, if using the superscript function is goofing up the whole line, I'd
just try typing it somewhere innocuous--say, at the very end of the document.
 Then, just type in the normal letters, click the superscript icon, type in
your -1, and then copy what you have typed.  Then, go where you want to
insert it, and click paste.
That way, you won't have to worry about superscripting the entire line.

I'm not sure I understood your qeustion, but does that answer it?  If not,
please clarify.

Hope this helps.

Paul

Try this:
Type and format the text as you want it to appear in the document (incl.
superscript). Then cut or copy the text (to transfer it to the Clipboard).
Select Edit > Find and Replace (Ctrl+H).
In the Find what field, type the string you want to replace (i.e. "Km/seg").
In the Replace with field, type "^c" (without the quotes).
Click Replace All.

Note that ^c will use the contents of the Clipboard as the replacement string.

Let's start from scratch, since you seem to have misinterpreted previous
answers:

1. Anywhere in the document (at the beginning is easiest), type Km/seg-1 (I
don't think you want a space between "seg" and "-1" if it's an exponent).

2. Select just the -1 and format it as superscript (Ctrl+Shift+= is the
keyboard shortcut for this).

3. Select the entire expression and Cut it to the Clipboard (Ctrl+X).

4. Ctrl+H to open the Replace dialog.

5. Type Km/seg in the "Find what" box.

6. In the "Replace with" box, type ^c (which is the code for "Clipboard
contents").

7. Click Replace All.