How would you mark out a masons mitre?

To mark out a mason's mitre, first, determine the angle of the mitre you need, typically 45 degrees for a square corner. Use a protractor or a mitre square to mark the angle on the material. Then, measure and mark the desired length along both edges of the material, ensuring that the marks intersect at the angle. Finally, use a straight edge to connect the intersection point to the ends of the marks, creating a clean line for cutting.