Chapter 20 The HP Model 9100A computing calculator 245

matically entered into the mantissa. Thus only two keystrokes [ENTER EXP] [6] suffice to enter 1,000,000. The CHG SIGN key changes the sign of either the mantissa or the exponent depending upon which one is presently being addressed. Numbers are entered in the same way, regardless of whether the machine is in FIXED POINT or FLOATING POINT. Any key, other than a digit key, decimal point, CHG SIGN or ENTER EXP, terminates an entry; it is not necessary to clear before entering a new number. CLEAR X sets the X register to 0 and can be used when a mistake has been made in a number entry.

ADD, SUBTRACT, MULTIPLY, DIVIDE involve two numbers, so the first number must be moved from X to Y before the second is entered into X. After the two numbers have been entered, the appropriate operation can be performed. In the case of a DIVIDE, the dividend is entered into Y and the divisor into X. Then the [ ¸ ] key is pressed causing the quotient to appear in Y, leaving the divisor in X.

One way to transfer a number from the X register to the Y register is to use the double sized key, [­ ], at the left of the digit keys. This repeats the number in X into Y, leaving X unchanged; the number in Y goes to Z, and the number in Z is lost. Thus, when squaring or cubing a number, it is only necessary to follow [­ ] with [´ ] or [´ ] [´ ]. The [¯ ] key repreats a number in Z to Y leaving Z unchanged, the number in Y goes to X, and the number in X is lost. The [­ ROLL] key rotates the number in the X and Y registers up and the number in Z down into X. [ROLL¯ ] rotates the numbers in Z and Y down and the number in X up into Z. [x¬ ® y] interchanges the numbers in X and Y. Using the two ROLL keys and [x¬ ® y], numbers can be placed in any order in the three registers.

The group of keys at the far left of the keyboard, Fig. 4, gives a good indication of the power of the Model 9100A. Most of the common mathematical functions are available directly from the keyboard. Except for [ô yô ] the function keys operate on the number in X replacing it with the function of that argument. The numbers in Y and Z are left unchanged. [Ö x] is located with another group of keys for convenience but operates the same way.

The circular functions operate with angles expressed in RADIANS or DEGREES as set by the switch above the keyboard. The sine, cosine, or tangent of an angle is taken with a single keystroke. There are no restrictions on direction, quadrant or number of revolutions of the angle. The inverse functions are obtained by using the [arcÑ ] key as a prefix. For instance, two key depressions are necessary to obtain the arc sin x: [arcÑ ] [TAN x]. The angle obtained will be the standard principal value. In radians:

The hyperbolic sine, cosine, or tangent is obtained using the [hyperÑ ] key as a prefix. The inverse hyberbolic functions are obtained with three key depressions. Tanh¹ x is obtained by [arcÑ ] [hyperÑ ] [TAN x]. The arc and hyper keys prefix keys below them in their column.

Log x and 1n x obtain the log to the base 10 and the log to the base e respectively. The inverse of the natural log is obtained with the e^x key. These keys are useful when raising numbers to odd powers as shown in one of the examples on the pull-out card, Fig. 3.

Two keys in this group are very useful in programs. [int x] takes the integer part of the number in the X register which deletes the part of the number to the right of the decimal point. For example int(-3.1416) = -3. [ô yô ] forces the number in the Y register positive.

Sixteen registers, in addition to X, Y, and Z, are available for storage. Fourteen of them, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, can be used to store either one constant or 14 program steps per register. The last registers, e and f, are normally used only for constant storage since the program counter will not cycle into