What I want to know is how (and where) can I find the properties of an individual face of an object. What I want to do is to work out the angle a particular face is at so that I can match another mesh/object to it.
Ive tried to do it manually by sight but cant get them to match exactly.
I think the Track To constraint is what you are looking for. With that constraint, that object will always face the one specified as being tracked to. Blender will automatically adjust the object’s rotation to face the other object. Well, on second thought, that isnt exactly what you want.
The way to figure out the face angle (actually two angles, ascension and declination) one relative to the XY plane (think of a ramp) and the other relative to the XZ plane (think twist like a radar) is by good old math using the vertex coordinates of the vertices that make up the face (3 or 4, you probably have 4). Technically, with 4 verts, your face is not geometrically flat, and Blender compensates somehow to make it look flat - probably by averaging the verts that are out-of-line. Take the difference in their XYZ locations, by, in Edit mode, selecting the vert and using the N key to see their properties. Then you will have your XY sets and XZ sets. Do the difference, use the sin() function on your calculator. If the top left vert is at XY 1,0 and the right is at XY 2,1, they are 1 unit in the X apart and 1 in the Y. COS(1/1) is 45 degrees.
Select your face… align the view to the selection (I think * did that)… place the cursor in your view, add an empty. Now because your view is aligned to the face, so will this empty be… so select object/select empty… ctrl+c… .copy rotation.
At least…that’s how I remember it… might be wrong about the shortcuts… but that’s the method.