Section 12: Subroutines186
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.
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 *

 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 *

 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.