Hi Kourosh – Had to do some digging on this – sorry for the delay.
When you choose ‘LaTeX’ as the main font, DataGraph uses the Latin Modern Roman font family. This is not just one font but different typefaces that are designed for different font sizes. This is unique to LaTeX fonts. The typeface varies for different size characters. For example, when you use a large font the characters are thinner. When you use a small font, the characters are wider.
By choosing the LaTeX main font, we do the work for you by selecting the proper type face depending on the font size. As you have noted, we have set this up for several discrete font sizes.
If you want to have more control, set the Main font to ‘Specify’. Click on the font name in DataGraph to open the Apple font picker. Then look for Latin Modern Roman. You will see not one font but different typefaces (from size 5 to 17) (See the attached Image).
If you wanted 21 point, you would choose the 17 typeface, since this is as high it goes. If you wanted to change to 8 point font and be true to the LaTeX font family you would have to pick the 8 typeface and set the size to 8 point.
The apple system really does not elegantly have a way to deal with the varying typeface which is why you have to pick both. As a result, there is nothing preventing you from using a typeface intended for small fonts, and set it to a larger font size.
We are looking at some new options for LaTeX fonts that would improve the look of greek characters. We will also consider adding a slider for the LaTeX option that would give you the flexibility you are looking for. For now, using the Apple font picker is the only way to use fonts outside of the ones we have set up for LaTeX.
Sorry for the long explanation! Hope that makes sense.