The units should change when you are changing a dimension. However, if you are using the measure tool it could be that you also need to change the dimensions for this which can be different from the document properties
So just to clarify, you are looking to dimension an angle that a line makes in units of degrees? Or are you creating a sinusoidal equation to define a line's length? It may be easier to take a snap of the part/line to explain what exactly you're going for.
When you are in the document properties, what unit system do you have selected? IPS/MMGS...? Also, just to check what you changed for document properties, did you do as follows:
Tools > Options > Document Properties > Units > Angle > Use the drop down menu to select degrees
or did you change that some other way?