Borrow carpenter's square

To use a carpenter's square for measuring:

1. Measuring Length:

Place one of the ruler's arms along the edge of the object you want to measure. Align the zero mark of the scale with one end of the object, and read the measurement where the other end of the object aligns with the scale on the ruler's arm. 

2. Marking Right Angles:

To mark a perfect 90-degree angle, align one arm of the square along a straight edge of your material. Use the other arm as a guide to draw a perpendicular line. 

3. Checking Squareness:

Place the inside corner of the square against the corner of a workpiece to verify if it forms a true 90-degree angle. If there are no gaps between the square and the workpiece, the corner is square. 

4. Laying Out Cuts:

For tasks like framing or roofing, the square can be used to lay out precise cut lines on larger materials, ensuring accurate angles for joints.