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Someone pointed out in another thread that this calculator is intended to be usable in exams and has an "exam mode" (which presumably provides only a very speci

Someone pointed out in another thread that this calculator is intended to be usable in exams and has an "exam mode" (which presumably provides only a very specific set of functionality) that cannot be exited without plugging into a computer. I wonder if the choice of a "no derivatives" license was motivated by the need for a legal tool to prevent distribution of altered firmware that can break out of exam mode without a computer. Funny side story: when I entered high school, the school recommended that everyone buy a Ti-83. Somehow my parents accidentally bought a Ti-89 instead. Unlike the Ti-83, the Ti-89 supports, out of the box: simplifying symbolic expressions (e.g. evaluating 2/4 to 1/2 instead of 0.5), solving arbitrary equations, solving systems of multiple equations and multiple unknowns, computing derivatives and definite/indefinite integrals of functions symbolically, and a lot more. I was never asked not to use the Ti-89 on any test, either in math class or on a standardized test. I don't think anyone administering the tests was aware that this calculator could basically do the entire test on its own if only it had something to write with. For what it's worth, I never cheated with it, not least because typing a complicated problem into the calculator generally took longer than just solving it by hand. I mostly used these fancy features just to see if the calculator knew how to solve whatever new problem we'd just learned in class. It almost always did.

aidenn0 9y ago
IANAL, but my understanding is that the exam mode could be fully protected by the trademark; the ND clause is not needed. Just like non-official builds of Firefox are limited in their use of the Firefox trademarks (thus iceweasel).
aidenn0 9y ago
The TI-89 was itself created as a new version of the TI-92, but without a qwerty keyboard, since the standardized tests banned all devices with a qwerty keyboard.
- acjohnson55 9y ago
  I bought one at a time when schools and tests hadn't quite figured that out yet :)
  - aidenn0 9y ago
    ... I'm not sure that's possible because the 89 was created specifically in response to the college board (and those that followed their lead) banning QWERTY keyboarded calculators.
    - acjohnson55 9y ago
      My hunch is that QWERTY was a shorthand for "too powerful". I'm pretty sure my math teachers were unaware just how sophisticated the 89's CAS capabilities were. Although I do see that the TI-89 is still allowed [1] on the SAT. [1] https://collegereadiness.collegeboard.org/sat/taking-the-test/calculator-policy https://collegereadiness.collegeboard.org/sat/taking-the-tes...
Gaelan 9y ago
Simple solution: codesign the “official” builds. Have a “test mode” LED on the device, and have the firmware refuse to turn the light on when running an unsigned build. Bonus points if you allow dual booting into the standard build for testing.
- exikyut 9y ago
  I've been pondering a similar problem to this - secure state verification - and it seems fundamentally hard. In the case of the LED, it would be simple to open the case and cut the trace to the LED. Now you have to put every single calculator into test mode to verify the LED lights up before you can start the test. That won't work.
  - revelation 9y ago
    You seem to be suffering from a rather common affliction in tech circles. Normal people do not care in the slightest if someone could open the calculator and cut the LED trace.
    - fasquoika 9y ago
      Yeah, this should be pretty clear from the parent post talking about the TI-89. It's almost impressive how little effort actually goes into preventing cheating. It's basically honor system + harsh threats
    - exikyut 9y ago
      For what it's worth, I'm actually trying to solve the problem of creating a verifiably secure device based on a tamper-resistant design at the moment, so that bias crept in a bit. I fully realize that what I'm trying to do (build a trustable boot path that's also hackable) is impossible to 100% achieve; I'm instead trying to see if I can build a super cheap design that's irritatingly expensive to circumvent (for a known value of "expensive", with hopefully 5 or 6 zeroes). It's a thought experiment at this point; I guess I'm practicing hammering every nail in sight with my ideas to test if my mindset is actually sane or not :P
  - 9y ago

aidenn0 9y ago

IANAL, but my understanding is that the exam mode could be fully protected by the trademark; the ND clause is not needed. Just like non-official builds of Firefox are limited in their use of the Firefox trademarks (thus iceweasel).

aidenn0 9y ago

The TI-89 was itself created as a new version of the TI-92, but without a qwerty keyboard, since the standardized tests banned all devices with a qwerty keyboard.

acjohnson55 9y ago
I bought one at a time when schools and tests hadn't quite figured that out yet :)
- aidenn0 9y ago
  ... I'm not sure that's possible because the 89 was created specifically in response to the college board (and those that followed their lead) banning QWERTY keyboarded calculators.
  - acjohnson55 9y ago
    My hunch is that QWERTY was a shorthand for "too powerful". I'm pretty sure my math teachers were unaware just how sophisticated the 89's CAS capabilities were. Although I do see that the TI-89 is still allowed [1] on the SAT. [1] https://collegereadiness.collegeboard.org/sat/taking-the-test/calculator-policy https://collegereadiness.collegeboard.org/sat/taking-the-tes...

Gaelan 9y ago

Simple solution: codesign the “official” builds. Have a “test mode” LED on the device, and have the firmware refuse to turn the light on when running an unsigned build. Bonus points if you allow dual booting into the standard build for testing.

exikyut 9y ago
I've been pondering a similar problem to this - secure state verification - and it seems fundamentally hard. In the case of the LED, it would be simple to open the case and cut the trace to the LED. Now you have to put every single calculator into test mode to verify the LED lights up before you can start the test. That won't work.
- revelation 9y ago
  You seem to be suffering from a rather common affliction in tech circles. Normal people do not care in the slightest if someone could open the calculator and cut the LED trace.
  - fasquoika 9y ago
    Yeah, this should be pretty clear from the parent post talking about the TI-89. It's almost impressive how little effort actually goes into preventing cheating. It's basically honor system + harsh threats
  - exikyut 9y ago
    For what it's worth, I'm actually trying to solve the problem of creating a verifiably secure device based on a tamper-resistant design at the moment, so that bias crept in a bit. I fully realize that what I'm trying to do (build a trustable boot path that's also hackable) is impossible to 100% achieve; I'm instead trying to see if I can build a super cheap design that's irritatingly expensive to circumvent (for a known value of "expensive", with hopefully 5 or 6 zeroes). It's a thought experiment at this point; I guess I'm practicing hammering every nail in sight with my ideas to test if my mindset is actually sane or not :P
- 9y ago