Section 12: Subroutines186
Finally, load the AREA program.
Keystrokes Display      
g GTO · · 
  00 REG 36    
     
g LBL 
       
     
ALPHA AREA ALPHA 
  01 LBLTAREA    
    The program name.
ALPHA HEIGHT? ALPHA 
  02THEIGHT?    
     
PROMPT ( Σ+ ) 
  03 PROMPT    
    Prompts and stops for input.
ALPHA RADIUS? ALPHA 
  04TRADIUS?    
    Prompts for data.
PROMPT ( Σ+ ) 
  05 PROMPT    
    Stops for input.
STO 08 
  06 STO 08    
  Computes area of top and bottom.
g X2 
  07 X  2    
 
g   
  08 PI    
 
 ×  
  09 *    
 
2 
  10 2 _    
 
 ×  
  11 *    
 
X Y 
  12 X<>Y    
 
Computes area of the cylinder without the top and bottom.
RCL 08 
  13 RCL 08    
 
 ×  
  14 *    
 
g   
  15 PI    
 
 ×  
  16 *    
 
2 
  17 2 _    
 
 ×  
  18 *    
 
 +  
  19 +    
    Gives the total area.
g GTO · · 
  00 REG 30    
     
We now have three programs in memory that help determine the heat loss from the water heater. AREA and TEMP, however, can stand alone as independent programs and you can run these to find just the area or temperature difference. BTU, on the other hand, uses AREA and TEMP as subroutines. If those subroutines do not exist in program memory when you run BTU, the program cannot run in entirety. The calculator will search for the labels, but if they cannot be found, it will display NONEXISTENT.
Run the BTU program now to find the heat loss (BTUs per hour) from a large cylindrical water heater with a height of 17.48 feet and a radius of 4 feet. The ambient room temperature is 79 degrees Fahrenheit and the temperature of the surface of the heater is 153 degrees Fahrenheit.