HP 35s Manual page 5

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HP 35s Using Register Arithmetic
apart from this, many users find that storage register arithmetic has important applications in programs. There are three
reasons for this.
(1) Each STO or RCL instruction takes one less step in a program than STO or RCL followed by a separate
arithmetic command. Saving a step in a program makes it shorter, faster and easier to read.
(2) STO arithmetic does not use the RPN stack and does not change the LastX register. This means that
programs can be written to work in the same way as built-in HP 35s functions, to replace the original
number with a calculated result, keep a copy of the original number in LastX, and leave the rest of the stack
unchanged. Such programs can then be used like built-in functions, and can be called from other
programs.
This training aid has shown how STO and RCL arithmetic can be useful in keyboard calculations and in programming.
With experience, users can find many occasions where storage arithmetic on the HP 35s is a real help in their work.
hp calculators - 5 - HP 35s Using Register Arithmetic - Version 1.0