Hi Dieter!

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The 34s requires nine seconds to return the two solutions:

Ooops, that's indeed a bit long! :-(

But this only if there are 2 solutions, for usual TVM problems with 1 solution the time should be less than 3 seconds, because only 1 instead of 3 SLV calls are needed, and I would say that this is acceptable.

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I observed two problems:

Well, I'm absolutely sure that it's not the fault of my program and I'm quite sure that it's also not the SLV routine. I'm calling SLV only when the interval of the 2 initial guesses has different signs on both ends, so the solver should always find a solution. And in fact in 99.9% of all examples I've tried the solver returns this solution - only in very rare cases (e.g. for interest rates < -99.9%) sometimes it doesn't find a solution. The reason is that for such unrealistic interest values the TVM expression may have really huge values (e.g. 10^30), and then SLV fails. But such I-values are clearly out of the valid range.

I rather guess there's a problem with your firmware build, but let's wait what Marcus gets on his WP34s.

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And finally, after pressing [B] the iteration starts, but the display continues to show its N I PV PMT FV message. Except the flashing RCL indicator there is no visible feedback to the user, telling him that a calculation is in progress. I would like to see something like "Solving..." while the interest rate is being calculated.

Yes, that may indeed be a good idea. The problem is that I only have the emulator, so solving for 'I' is done in a fraction of a second and for me this message disappears immediately

What would you prefer, just delete this 'N I PV PMT FV' display or really showing 'Solving..' (which would require more bytes of course)?

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BTW: In the current version, the [A] key is used to enter values as well as to start their calculation. What about two keys, say [A] and [B] - one for storing values and the other to have them calculated? Like a [SET] and [COMPUTE] button, similar to what is found on other brand calculators. This way we would also get rid of the cumbersome ENTRY? test and the one or other additional [R/S] to clear the entry flag.

That's an idea which I won't like very much. AFAIK all financial HP calculators work exactly this way, i.e. if you've entered a value before pressing those keys the value is stored, else it is calculated. I would say that's the most simple method, and shouldn't the WP34s be as compatible as possible to all other HP calculators?

BTW, if you've entered anything previously and then want to calculate any of the 5 TVM values, there's no need to press [R/S] before - you can just press [A][?] twice: the 1st press stores the value, but the 2nd press calculates it.

Franz

*Edited: 25 Dec 2012, 4:17 p.m. *