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Register Arithmetic

Register Arithmetic

The HP Palmtop's Calculator has 10 registers for storing and recalling numbers. You can make the first five registers appear on the screen in the Arithmetic sub-application by pressing [Menu] Options Calculator Modes and pressing E' (You can also force the calculator to show the stack by pressing T'.) There may also be "named registers" available when you're using a Solver equation-more about these later.

Whether or not the registers are visible on the screen, they're available for use in many of the other sub-applications. For example, in Calc press CTRL+O to start the Conversion sub-application. Press L to open the Length Conversion window. Key in 10 and press F2[mile]. Now, suppose you want to compute the ratio of feet to US survey feet. Here's the way to do this with Register Arithmetic.

Press M[Rcl] F4[Foot] N[Sto]3 (see Reg3=52,800.00 in the calc line). Now press F10[More] and press M[Rcl] F8[ft US] (see ft US = 52,799.89). Press N[Sto]/3 and M[Rcl]3 and see Reg3 = 1.00. Press [Menu]Options Number Format 9 Enter and M[Rcl]3, again to see Reg3 = 1.00000200. This value will be available for further computations in register 3 until you change the contents of the registers or clear all the registers. Of course, you don't need to do register divide for this example. You could simply Rcl foot and Rcl ft US and press the divide key. Either method will get you the desired result.

Register 0 is a special register. It acts like the Memory register available on many inexpensive pocket calculators. In the Arithmetic application you can use the F7 key to store a value in Reg0. The F8 key recalls the contents of Reg0 to the calc line and F9 and F10 perform Memory addition and subtraction.

In Solver, and the other sub-applications that assign variable names to the function keys, you can use N[Sto] (optionally followed by + - * /) and then press a named function key.

In effect the 10 built-in registers and all the named variables can act as independent calculators that can perform simple arithmetic operations.

For old-hands who were weaned on the likes of the HP 41C calculator, such storage arithmetic was a very handy trick. And, if memory serves me correctly, the HP 41C even let you perform storage arithmetic on the stack registers (something HP Calc won't do). I also recall that on the 41C you could use RCL+ and RCL. I suppose HP decided to omit these features to protect the sanity of its customers.

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