Bug: HP Prime can't do Log's

[davimle]

I bought my daughter (who is a Sophomore in H.S.) an HP Prime when she needed a graphing calculator, instead of the TI-84 that is recommended (and used by everybody else in her class), partly because it seems to be a superior machine (touch screen, graphing speed, display, CAS mode, etc.) and partly because my wife and I are both engineers and we both loved our HP 28S calculators from our days at the university.

However, aside from the fact that the HP Prime doesn't solve quadratics as easily as the TI-84, we have run into what seems like a pretty basic bug (which may be a deal-breaker). The Prime can't do Log's of arbitrary base and get the right answer! Luckily my daughter is pretty good at math and pointed out to me that the calculator is not getting the right answer, rather than blindly believing the result. This can be quite a pain in more complex formulas, and also leads me to question what else does the Prime get wrong?!

Here are some really simple examples: (Again, math that underclass students in H.S. should get right.)

Log(base 3) of 81. Answer should be 4. (81 = 3^4)
Log(base 5) of 125. Answer should be 3. (125 = 5^3)

However, this is what the Prime returns:

Code:

  LOG(81,3)  = 3.99999999999
  LOG(125,5) = 3.00000000001

When suggested by HP support, switching to Engineering or Scientific display mode, it seems to get the right answer:

Code:

  LOG(81,3)  = 4.00000000E0
  LOG(125,5) = 3.00000000E0

However, since fewer digits are shown, this just seems to be a case of rounding. (e.g. with the first one, doing ANS - 4 returns -1.00000000E-11 just as one would expect.) So this doesn't feel like the a real solution. In addition, my daughter hates Scientific or Engineering mode and immediately switched it back to Standard. I have not had much luck with HP Support, in fact one representative insisted that the answers returned by the calculator were correct and that they were simply more precise. It's a shame that people in the US can't do math, perhaps this is one area where having support outsourced to India would mean getting someone who knew what the right answer was?

Both the market leader (TI-84) and a low-cost alternative (Sharp) calculator return the correct answer to both of these examples. It makes me sad that the HP Prime cannot. It is even more infuriating that HP support doesn't seem to understand that a calculator that can not calculate a correct answer is not worth much (even with color, fancy touch screens, etc.) In the area of math, there still is a right vs. wrong answer, rather than just being "opinion" or "close enough" unlike so many other things these days. (Anybody else remember Pentium FDIV?)

So I wanted to know: 1) Has anyone else run into this problem? and did HP seem to understand the gravity of the situation? and perhaps more importantly 2) Have others gotten wrong answers to other calculations that we should know about?

Thanks in advance. I'm currently torn between waiting and hoping that HP will come up with a fix, or returning the calculator as defective and being a "sheep" by getting my daughter a TI-84 Plus CE.