This controls how proportional fonts are scaled, and only applies to GUI extensions (buttons, edit boxes, checkboxes, static text controls, etc.) which may or may not be present in your application. (As of build 974, it also only applies to GUI font objects on the main window; those inside of dialogs are controlled by a corresponding option on the Dialog Sizing dialog.) The standard fixed pitch fonts are always scaled according to the window size, but this is not necessarily desirable with the proportional GUI fonts. It is actually quite rare for Windows applications to change the size of the fonts according to the size of the window. In fact, it is rare for Windows applications to even adjust the spacing of controls when changing the window size. In the case of A-Shell, in order to keep GUI objects (including static text controls) synchronized with the fixed pitch character grid, we always adjust the spacing of objects when the window is resized. But the question is whether to adjust the font sizes as well.

For the most Windows-like effect, set the scaling to 0. This will result in the standard Windows control font (a sans serif font similar to Arial or Helvetica, which is called MSDialog in WindowsXP and Segoe UI under Vista). Since its size will not change with the window size (if the scaling factor set to 0), while the size of fixed pitch text and certain container objects, such as buttons and edit boxes will change, you will probably want to adjust your Window size until the fonts seem to fit best. (The larger the window becomes, the more space the fonts will have to fit into their containers, but at the same time, the difference between the size of the proportional fonts and any fixed pitch fonts will increase. Once you determine the most desirable window size, save your settings (File..Save).

If you want to be able to make the fonts bigger on demand simply by maximizing the Window, then set the scaling factor to something in the range of 80 to 100. This will cause the proportional fonts to scale up and down according to the window size. Note, however, that font scaling is not totally linear, so you may find that with large window sizes, you need a smaller scale factor, say 80 to make things fit, than you do at smaller window sizes. (Again, the idea is tinker with the scale factor and window size until you get a pleasing combination, then save it.)