WP31s error recovery

[Dieter]

(03-02-2015 07:57 AM)BarryMead Wrote:  You can see that the UNDO really does restore the actual "STACK" but in your example the number 4 was not yet in the stack (only in the input register) so the UNDO couldn't restore it. In your example the actual X register still had the 3 in it from [ENTER] duplication, and the input register (displayed in the lower line of the calculator) does not show what is in the X register It shows the partially completed input register (4). If you run the QT emulator for the WP-31s you can see this in real time.

Barry, that's a very interesting observation. However I do not think this is the way the 31s should behave. It is an ultimately "classic" RPN device, and the documentation does not know of an input register as opposed to the usual stack register X. In the first example, the [ln] key computes the natural logarithm of X, so there must have been a –4 in X before. Likewise the [+] key adds Y and X, so again there must have been a 4 in X. And finally there is a LastX command (OK, RCL L in this case) that restores the X-value before the last operation.

So I do not think that the examples show the behaviour intended by the 31s team. Pauli? Walter?

Dieter