: 1. If there is a right-angle protractor, measure with it; If there is a right-angled square box on the platform, you can draw parallel lines with a ruler to measure it.

2. If it is a large steel plate, use a universal ruler (box ruler/tape measure): ① For a large square (rectangular) steel plate, use the diagonal method to measure. If the diagonals are equal, it is a right angle, otherwise it is not a right angle. (2) If one side has a right angle and the other side has an irregular shape, it is measured by the principle of twisted string (3 strands, 4 strings and 5 strings). If two right-angle measuring sides A = 3m and B = 4m, then the detection of hypotenuse C should be equal to 5m. If the equation is invalid, it is not a right angle. (3) If it is a large right-angle steel plate, use the diagonal method and the Pythagorean chord method above, and use a laser rangefinder to measure and check the right angle.