SM421 Operation HandbookPART VI Additional Check Points593. Checking the flatness of the PCB1. Checking the flatness of the PCB in a diagonal direction 2. Checking the flatness of the PCB in a horizontal direction- Place and secure the PCB in the conveyer. Then, check if the PCB is flat using a ruler.- Use a ruler to check if the PCB is flat diagonally. - Use a ruler to check if the PCB is flat in three horizontal positions.PART VI. Additional Check PointsIf the PCB is not flat, the parts may not be properly placed. If the PCB is not flat, reset the height of the backup pins.Caution