11-30-2014, 08:51 PM

This is a proposal for a new feature for the WP34S.

I wonder, why I never heard about the idea of a LastXY register in RPN Calculators.

Obviously the more than fourty year old LastX register works perfectly for correcting a misexecuted monadic function like X^2. But for dyadic functions the user has to think about the correct inverse function of that he just has executed, and he has to enter it explicitely by an extra keystroke and some extra keystrokes for recalling the LastX register twice. Nobody would have difficulties to find the inverse function of x + - / etc., but still there is more comfort without having to think about it. Even more important is, this procedure does not always produce the exact Y value as it was before the operation. Think of multiplying after having done a division or worse.

If you would give the user a dedicated LastXY register, accessible by typing RCL U, if you like to call it Undo Register, which restores both, X and Y register, like they were just before the last operation, the user can forget about which operation he just executed, has the full precision, and can easily type the new dyadic function.

Even better in my opinion could be the implementation, that RCL L restores automatically either X or XY register depending on the last executed function, which the WP34S knows, was either a monadic or a dyadic function.

Of course, this could make old programs, that use the LastX functionality, become incompatible, but the advantage of having improved a fundamental old feature, which it not longer limited by available memory, could be worth of thinking about an implementation, couldn't it?

I wonder, why I never heard about the idea of a LastXY register in RPN Calculators.

Obviously the more than fourty year old LastX register works perfectly for correcting a misexecuted monadic function like X^2. But for dyadic functions the user has to think about the correct inverse function of that he just has executed, and he has to enter it explicitely by an extra keystroke and some extra keystrokes for recalling the LastX register twice. Nobody would have difficulties to find the inverse function of x + - / etc., but still there is more comfort without having to think about it. Even more important is, this procedure does not always produce the exact Y value as it was before the operation. Think of multiplying after having done a division or worse.

If you would give the user a dedicated LastXY register, accessible by typing RCL U, if you like to call it Undo Register, which restores both, X and Y register, like they were just before the last operation, the user can forget about which operation he just executed, has the full precision, and can easily type the new dyadic function.

Even better in my opinion could be the implementation, that RCL L restores automatically either X or XY register depending on the last executed function, which the WP34S knows, was either a monadic or a dyadic function.

Of course, this could make old programs, that use the LastX functionality, become incompatible, but the advantage of having improved a fundamental old feature, which it not longer limited by available memory, could be worth of thinking about an implementation, couldn't it?