Section 12: Subroutines187
Keystrokes Display    
PRGM 
  0.0000    
  Takes the HP-41C out of PRGM mode.
XEQ 
       
   
ALPHA BTU ALPHA 
  HEATER?    
   
152 
  152 _    
   
R/S 
  AIR?    
   
79 
  79 _    
   
R/S 
  HEIGHT?    
  The second root.
17.48 
  17.48 _    
   
R/S 
  RADIUS?    
4 
  4 _    
   
R/S 
  LOSS=18,522.2975    
  Btu per hour.
If you want only the temperature difference or the area, run just those programs (TEMP of AREA). Run BTU again for a water heater that is 6.2 feet high and has a radius of 1.1 feet. The room temperature is 66 degrees Fahrenheit and the temperature of the surface of the water heater is 89 degrees Fahrenheit.
Keystrokes Display    
XEQ 
       
   
ALPHA BTU ALPHA 
  HEATER?    
   
89 
  89 _    
   
R/S 
  AIR?    
   
66 
  66 _    
   
R/S 
  HEIGHT?    
  The second root.
6.2 
  6.2 _    
   
R/S 
  RADIUS?    
1.1 
  1.1 _    
   
R/S 
  LOSS=545.4075    
  Btu per hour.
g CLX 
  0.0000    
   
Subroutine Limits
A subroutine can call up another subroutine, and that subroutine can call up yet another. In fact, you can have up to six subroutine branches before returning to the first program. Subroutine branching is limited only by the number of END s or RTN s that can be held pending by the calculator. Six subroutines can be held pending at any one time in the HP-41C. The illustration below make this more clear.