The values on the calculator that we use for common roof framing are: Pitch, Rise, Run, and Diagonal. If you have any two of those values, the calculator will quickly figure out the rest of the right triangle—which means it will tell you everything else you need to know about a rafter.
Most of the time, the two values I have are the run of a building and a specified pitch, which is why I used these values for the example in this online tutorial:
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