I'm looking for a reading ruler for Mac OS X.
To be precise: I don't want to measure something. I have to read long texts, which can be very exhausting. A line or marker which is easy to move would help a lot to keep the eyes on the right line.
There is a Firefox
extension called Paragrasp enabling you to read web pages with a marker.
Here is a short decription:
This Firefox extension adds a highlight to the paragraph you're reading, and with a single keystroke, moves to the next, automatically scrolling the page for you. Features include key configuration, color customization, mouse hiding, and control over scrolling position.
When you read PDFs, the free and open-source Skim offers a Reading Bar. Turn it on by going to View » Show Reading Bar, or pressing Shift-Cmd-B.
You move it up and down by Alt - ↑ and Alt - ↓.
In Preferences » Display, you can change its color or invert it.
I found this screen ruler. It's possible to configure it to show only the horizontal ruler and use it as a reading line.