How to lay out a common rafter with a carpenter's framing square - Imperial

How to lay out common rafters for a simple gable roof using a carpenter's framing square in imperial measurements (feet and inches).  Explanation of the roof triangle and basic roof framing terms used in Canada.  Shows the step-off method, and the 'calculate the line length' method. Originally made for a carpentry pre-apprenticeship college course. Goes with a worksheet for a practice rafter.