How do I type an "s" with a horizontal line above it for a medical form?

You can find the Keyboard Viewer living in input preferences. I keep mine up on the menu bar.

Go to SystemPrefs>International, and click on the InputMenu tab. Check the box for Keyboard Viewer (might as well include Character Palette as well), and check the box at the bottom for "show input menu in menu bar". You can have other languages show up there too.

Once that's done, just open Keyboard Viewer and you can see your whole keyboard, which reacts to what you hold down -- hold down the option key, e.g., and you'll see all the available characters. Easier to see that to describe. Give it a shot.

Where I used Helveitca Condensed the - is to the right of the character by about 1/2 space which tells me it is an added accent rather than a character built into the font.

s̄ does not have its own codepoint in Unicode, and must always be put together in some fashion by the font, so you will probably find that some fonts in some apps do it very well, while others can't do it at all.

Perhaps this article will help.

OPTION+a, followed by s works for me->s̄ (OPT+a, followed by SHIFT+s, to get S̄. Another one is OPTION+e followed by s to get ś.

Don't confuse him with the facts. He's already stated that Keyboard Viewer is useless for this task, but doesn't know that's what I used for the solution. 🙂