Check them with a framing square or measure so the lines are parallel with the rake ends.
Roofing using half tab method.
The cut outs separating the shingle tabs line up every other course.
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The simplest way to do this is to use the half tab offset method.
Mark the center of each section and use a compass to mark 30 degree angles along the sides of each.
Set the first shingle of the second row back a half tab 6 inches 17 centimeters from the edge of first shingle on the first row and so that the bottom of its tabs just touches the tops of the cutout slots on the shingle below.
Use a heavy duty utility knife to separate the shingles into thirds by cutting them at each tab.
For example if you re roofing from left to right align the first shingle of the second course so the right side of the shingle.
For a racking or midroof pyramid layout method snap two vertical lines called bond lines near the center of the roof the appropriate distance apart.