May 17th, 2004

math

Scientificalating up a glorified abacus

My scientific calculator has four memory function keys:
  • STO, which stores the displayed number in the memory;
  • RCL, which displays the number that's in the memory;
  • ADD, which increments the number in memory by adding the displayed number to it;
  • EXC, which swaps the displayed and memory numbers.

Meanwhile, my mom's checkbook calculator has four rather different memory functions:
  • M+, which adds the displayed number to the memory;
  • M-, which subtracts the displayed number from the memory;
  • MR, which displays the number that's in the memory;
  • MC, which clears the memory.

(Actually, it does this with only three buttons; MR and MC are combined in a single button, labeled MRC; one push displays the memory, a second push clears it.)

One day I was playin' around with a checkbook calculator, and I noticed that while M+ and MR work the same as ADD and RCL, respectively, I was annoyed at the lack of a counterpart for STO and EXC, which I consider wonderfully useful. Then I thought, hmm, I wonder if it's possible to simulate STO and EXC; that is, could I invent a series of button presses that would have the same result as those two functions?

I quickly figured out that all I had to do was simulate EXC. Then the STO problem would also be solved, by simulating EXC and then pressing MR. So... how to simulate EXC?

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