Which method provides a tool-free check for a 90-degree cabinet corner?

• A. Diagonals are equal.
• B. Use a framing square.
• C. Measure interior angle with a protractor.
• D. Check by aligning with a straightedge across the face.

Answer: (A)

When a cabinet corner forms a perfect right angle, the opening behaves like a rectangle. A key property of rectangles is that the diagonals are equal in length. So, by comparing the two diagonal distances across the corner opening, you can confirm the angle is 90 degrees without using a dedicated measuring tool. If those diagonal lengths match, the corner is square; if they don’t, the angle isn’t at 90 degrees and needs adjustment. This approach avoids tools like a framing square or protractor, making it a practical tool-free check.