Introduction 9
To calculate the heat loss of the water heater, merely press the following keys in order.
 Keystrokes Display 15 ENTER 15.0000 Temperature difference. 30 30 _ Area of water heater (sq. ft.). × 450.0000 Intermediate answer. .47 .47 _ Coefficient of heat transfer. × 211.5000 Heat loss in Btu per hour.
Programming the Sample Problem
The water heater in the example loses about 212 Btu every hour at the 15-degree temperature difference. Suppose you decide to calculate the heat loss of the water at many temperature differences. You could calculate the heat loss manually for each temperature difference. Or an easier and faster method is to write a program that will calculate the heat loss for any temperature difference.
Now let’s write, load and run a program to do just that!
Writing the program. You have already written it! The program is the same series of keystrokes you executed to solve the problem manually. One additional instruction, a label, is used to define the beginning of the program.
Loading the program. To load the instructions of the program into the HP-41C:
Press the following keys in order. The display shows symbols or names representing each instruction entered. The calculator records (remembers) the instructions as you entered them.
Keystrokes
PRGM    Places the HP-41C in PRGM (program) mode. The annunciator will show in the display to let you know that the HP-41C is now in PRGM mode.
g GTO · ·    This prepares the calculator for the program.
g LBL
ALPHA HEAT ALPHA    Defines the beginning of the program and names it HEAT.
 30  ×   .47  × The same instructions you executed to solve the problem manually.