Section 1: Getting Started24
• When you press and hold a function key for less than about a half second, the calculator displays the function name and then executes the function when you release the key.
• When you press and hold a function key for more than about a half second, the calculator first displays the function name and then displays NULL. The function is not executed when you release the key.
For example, to calculate the number of square meters in a 160-meter square field (160′ × 160′ or 1602):
 Keystrokes Display 160 160 _ g X2 25,600.0000 The answer.
Now, to find the square root of that result:
 Keystrokes Display 250,600.0000 Number from the previous operation. 160.0000 The answer.
and X2 are examples of one-number function keys; that is, keys that execute upon a single number. All standard HP-41C functions operate upon either one number or two numbers at a time (except statistics functions like Σ+ and Σ- —more about these later).
One-Number Operations
To use any one number function:
• Key in the number.
• Execute the function.
For example, to use the function 1/x, you first key in the number represented by x, then press the function key 1/x. To calculate ¼, key in 4 (the x-number), and press 1/x.
 Keystrokes Display 4 4 _ 1/x 0.2500 When you press and release 1/x, the function is executed.