When I switch to Fullscreen mode the ruler width is reduced to 5 inches and I can’t make it any wider. In regular editor mode the ruler widens in response to making the application wider. I want to write in Fullscreen mode, but I want the width of the writing space to be greater than 5 inches. How can I adjust the width of the ruler in fullscreen mode?
Assuming you mean the full screen mode on Lion, you may just need to edit the fixed width settings in the Preferences. Under the Editor tab, you can adjust the settings in the default editor width–either make them wider or deselect the option to use it at all (it’s probably just set to use it in full screen, since the editor space becomes so much wider there that it can be distracting for some users to have the text span such a distance). I’m on Snow Leopard now or I’d take a screenshot to show you this, but it should be fairly straight forward.
If you mean composition mode (which used to be called full screen, prior to Lion), drop your cursor to the bottom of the screen and a control panel will come up which contains a slider to adjust the page width.