I used mill rule when I was taught in my class. I suppose that's the easiest to teach a newbie. As has been said, few timbers are actually straight, thus the need for other layout methods. I am confident I understand square rule, but have yet to practice it(soon...). Precise measurements were stressed in my class to give nice tight fitting joints. It would seem that it would be more difficult to be so precise with measurments, given the width of chalk lines and having to judge the center of a chalk line. This leads to housing the joints according to what I have read. This is understandable, but I have one question... If you are putting a mortise in your second (tertiary) reference face, what technique do you use to measure the depth of your housing (the face) relative to the Chalk line on your Primary face? How do you hold the squares? It would seem kind of awkward to try and hold your framing square to your Primary reference face at a set distance from your Chalk line, and then hold your machniist square on the narrow tongue of the framing square measuring the depth. Am I incorrect in how to do this? I suppose I must clarify in that the housing is a full housing whereby you cannot just measure from the edge to the chalkline.