According to the national standard, the overall bow of flat tempered glass should not exceed 0.3% and local wave should not exceed 0.2%. The flatness of tempered glass is one of the major indicators of the glass quality.

The wind board in the air distribution box can be used to adjust the flatness of tempered glass. The pointer indicates zero value when the wind board stays at the middle position of the air distribution box, while it indicates positive value when the wind board moves upwards and negative value when it moves downwards. If the tempered glass bend upward, it means the top air pressure of the chiller is not strong enough, in this case the wind board should be moved downwards, i.e., towards the direction of negative value. If the tempered glass bend downward, the wind board should be moved upwards.