Click Calculation options in the fire resistance calculator menu to open the Thermal Calculations Parameters dialog. 
The following options are available. 
- Parameters of a calculation grid created in the cross-section of an RC element. 
- Division of the cross section area in the X and Y coordinates (specify a number of edge divisions along the axes X and Y) 
 
- Approximation of the cross-sectional contour. 
-  Underapproximation. 
 
 
- Overapproximation. 
 
 
  
  
- Time increment step is a value of the time step in thermal calculations.