Can not enter exact dimensions

Hello, I’m a new user sampling the Layout. A very basic question: I can’t seem to get Dimensions work. In Preferences, I have selected a scale of ¼"=1’. Under File>Document Setup, I have selected Fractional. I then make sure the Dimension Tool is selected. Now at the Dimension window, I see the scale I’ve selected does indeed appear. But when I attempt to dimension a drawing, it does not correlate. For example, as I draw a dimension, when I’ve drawn ¼" worth of line, it shows 1’7"? I’m wondering what I’m missing or doing wrong? I’m using Mac OS X