How does on enter scientific type things like Mu µ into a text element in SD?

Find someplace where you can copy it from, and then paste it. If you don't find it anywhere, you can find the HTML entity using the HTML Editor.
It should also be possible to use the 'content' code box on the Element pane and write the HTML entities there.

Here is a wee example of what I wrote in the last sentence of my previous post. I had some Turkish letters handy, so I used them for this demo. View it first in SD, then in a browser.

Thanks Inger. Round about but can get the character in.

If you are in windows you can search on your computer for the "character map" tool. That lets you copy characters.

I forgot, you may need to select the Arial font in the tool if it isn't selected already. At the bottom you should have unicode for the Character Set. You can actually do a search for "mu" or scroll down the to the Greek section of the font. The regular Arial font should be good enough. If not, Arial Unicode MS has everything? Pretty close.