It is measured with a 90 degree steel square with an internal angle perpendicularity tolerance of 0.13mm and an internal angle side length of 500mmx400mm. Place the short side of the square against the short side of the plate, and the long side of the square against the long side of the plate. Use a feeler or vernier to measure the maximum gap between the long side of the plate and the long side of the square.
When the long side of the plate is less than or equal to 500mm, any pair of diagonal corners of the plate can be measured; when the long side of the plate is greater than 500mm, the four corners of the plate can be measured.
The measured value of the maximum gap represents the angle tolerance of the sheet. The measured value is accurate to 0.1mm.
