Ruler guides are different from grids in that they can be positioned freely on a page or on a pasteboard. You can create two kinds of ruler guides: page guides, which appear only on the page on which you create them, or spread guides, which span all pages and the pasteboard of a multiple-page spread. You can drag any ruler guide to the pasteboard. A ruler guide is displayed or hidden with the layer on which it was created.
New ruler guides always appear on the target spread. For example, if several spreads are visible in the document window and you drag a new guide into the window, the new guide becomes visible only on the target spread.