LVLINCR

     LVLINCR specifies the freezing level increment. Freezing level ranges
     are rounded to the nearest levels with the increment. For example, 
     if LVLINCR is set to 500, top freezing level of 8200 foot will be 
     rounded to 8500 foot. Bottom freezing level 4100 foot will be rounded 
     to 4000 foot.

     The default value is 500.