Due to the contact between the glass and the rollers in the glass tempering furnace, the lower surface of the glass will expand faster than the upper surface. Therefore, the glass will bend upwards and only the middle section of the glass is in contact with the roller of the glass tempering furnace resulting in a faster rise in temperature of this section (the principle of thermal conduction). The sections hanging in the air will only be in contact with the rollers to continue absorbing heat after the glass plates completes the softening process. At this moment, the heat in the middle of the glass is much more than the upper surface of the glass. This has resulted in a severe deformation followed by optical distortion because of temperature differences. At this point, the speed of the convectional blowers in the upper section of the glass tempering machine should be properly increased or the upper and lower furnace temperature should be adjusted accordingly, allowing the glass to be rapidly flattened in the glass tempering furnace so that the issue can be rectified in a timely manner.